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Rats respond to configurations of stimuli.

There are many studies on stimulus classes formation in pigeons and rats. They make it clear that both pigeons and rats have an ability to form stimulus classes between stimuli in either two concurrent discriminations (Delius, Ameling, Lea, & Staddon, 1995; Dube, Callahan, & Mcllvane, 1993; Nakagawa, 1978, 1986, 1992a, 1998, 1999a, 1999b, 1999c, 2001) or matching- (or nonmatching)-to-sample discriminations (Aggleton, 1985; Edwards, Jagielo, Zentall, & Hogan, 1982; Lombardi, Fachinelli, & Delius, 1984; Mumby, Pinel, & Wood, 1990; Nakagawa, 1992b, 1993a, 1993b, 1999d, 2000a; Rothblat & Hayes, 1987; Urcuioli, 1977; Urcuioli & Nevin, 1975; Urcuioli, Zentall, Jackson-Smith, & Steirn, 1989, Experiment 3; Vaughan, 1988; Zentall & Hogan, 1974, 1975, 1976; Zentall, Sherburne, Steirn, Randall, Roper, & Urcuioli, 1992; Zentall, Steirn, Sherburne, & Urcujoli, 1991), or same-different discriminations (Cook, Cavoto, & Cavoto, 1995, 1996; Cook, Katz, & Cavoto, 1997; Cook & Wixed, 1997; Edwards, Jagielo, & Zentall, 1983; Fet terman, 1991; Nakagawa, 1993a, 2000b; Santiago & Wright, 1984; Wasserman, Hugart, & Kirkpatrick-Steger, 1995; Wright, Santiago, Sands, Kendrick, & Cook, 1985; Wright, Santiago, Urcuioli, & Sands, 1983; Young & Wasserman, 1997; Young, Wasserman, & Garner, 1997)

Nakagawa (1992a, 1993b, 1999d, 2000b) has asserted that the mechanism of stimulus class formation between the discriminative stimuli in either concurrent, matching- (or nonmatching)-to-sample, or same-different discriminations was the same one, in which stimuli or stimulus configurations that are associated with the same outcome (e.g., food or no food) will come to be classed together (despite their perceptual dissimilarity) and it is these stimulus or configuration associations that mediate the transfer of appropriate responding to a subsequent shift problem. The basic idea of Nakagawa's proposal that a common response mediates concepts of matching and nonmatching, or sameness or difference to subsequent shift problems assumes that the novel stimuli and novel configurations appearing in the transfer tests generate the same mediator (i.e., common response to configurations of stimuli). These proposals are supported by the findings of both Experiment 2 in Nakagawa (1 999d) and Nakagawa (2000a, 2000b). A specif ic question, however, remains. Do rats respond not only to a stimulus itself but also to a configuration of stimuli? This is a very important and fundamental issue in behavior analysis in studying stimulus classes formation in rats. This problem has received far too little experimental attention in concurrent discrimination, matching- (or nonmatching)-to-sample discrimination and same-different discriminations. To demonstrate directly that rats respond to configuration of stimuli, it is necessary to investigate whether or not a framework of stimuli or stimulus configuration affects rats' perception, that is, whether or not rats have illusory perception.

Studies on form perception in animals have indicated both similarities and dissimilarities with form perception in humans. Blough (1982, 1985) has asserted that judgments about letter similarity are alike in pigeons and humans. By contrast, Allan and Blough (1989) have indicated that pigeons and humans respond differently to certain features of forms in visual search tasks.

Although many researchers have been interested in illusory perception by humans and many different geometric illusions have been discovered, there are few reports of illusory effects in animals. Dominguez (1954) showed that monkeys experience a horizontal-vertical illusion in which vertical lines are judged to be longer than horizontal lines of the same length. Dominguez (1954) further indicated that monkeys are likely to see rectangles as being taller than squares. Benhar and Samuel (1982) showed that anubis baboons see a Zollner illusion. Bayne and Davis (1983) showed that rhesus monkeys are susceptible to the Ponzo illusion, in which the position of bars within converging lines influences their perceived length.

Malott, Malott, and Pokrzywinski (1967) and Malott and Malott (1970) have addressed the Muller-Lyer illusion in pigeons. Malott et al. (1967) and Malott and Malott (1970) trained pigeons to respond on a horizontal bar of a particular length with two vertical lines on both ends. They were subsequently tested with bars of various lengths, which had inward or outward arrows on both ends. For the figures with the inward arrows, response rate peaked at a value greater than the training figure, as would be expected for the illusion. However, for the figures with the outward arrows, response rate peaked at the same length as that used in the training figure. Thus, evidence for the illusion was ambiguous.

When we observed two identical parallel bars located between two lines that make an inverted V shape, the bar nearer the apex of the lines looks longer. This phenomenon has been called the Ponzo illusion. Fujita, Blough, and Blough (1991) demonstrated that pigeons perceived the Ponzo illusion. In their Experiment 1, pigeons had difficulty in learning a simultaneous discrimination between converging context lines only when the Ponzo illusion could decrease the perceived differences in bar length. And then, in their Experiments 2 and 3, when pigeons were trained to report the length of a single bar located between converging lines, they tended to report "long" as the bar approached the apex of the converging context lines. Fujita, Blough, and Blough (1993) also demonstrated that the magnitude of the illusion varied almost linearly with the ratio of the length of the stimulus bar to the gap between the bars and the context lines. In this experiment, pigeons discriminated the length of a bar located between two c ontext lines. Responses to one key were reinforced when the bar was longer than a predetermined length, and those to the other key were reinforced when the bar was shorter. The inclination of the context lines was systematically varied 54.6[degrees] (converging upward) to 125.4[degrees] (converging downward). Of 6 pigeons, 5 tended to report "long" when the bars were located near the apex of the context lines, regardless of whether the context lines were oriented upward or downward. The magnitude of the illusion varied almost linearly with the ratio of the stimulus bar to the gap between the bar and the context lines. In pigeons, the magnitude of the Ponzo illusion changes with the inclination of context lines, reaching a maximum at an inclination of about 54.6[degrees] and 125.4[degrees].

The basis of the Ponzo illusion is, however, not clear in the case of humans. There is an argument over whether the Ponzo illusion is a depth/space/perspective illusion or a variant of the Muller-Lyer illusion. That is, the extent to which rotation of a display reduces the illusion is interpreted as evidence that the illusion is a perspective illusion, whereas the extent to which rotation of the display does not reduce the illusion is interpreted as evidence that the illusion is a case of the Muller-Lyer illusion.

Nakagawa (1999d) indicated positive transfer effect of learning between concurrent and matching- (or nonmatching)-to-sample discriminations in rats. Nakagawa (2000b) indicated positive transfer effect of learning between matching- (or nonmatching)-to-sample and same-different discriminations in rats. Nakagawa (1999d, 2000b) asserted that these positive transfer effects were caused by control of a framework of stimuli (i.e., stimulus configuration) but not by control of a discriminative stimulus itself. These findings of Nakagawa (1999d, 2000b) suggest that it is possible for rats to see the Ponzo illusion. However, there are no reports of illusory effects in rats. A special question, however, arises. Do rats see the Ponzo illusion as do pigeons? When rats saw the Ponzo illusion, was it a perspective illusion, or a variant of the Muller-Lyer illusion? The extent to which rotation of displays did not reduce the Ponzo illusion would be interpreted as evidence that the effect was not a perspective illusion, rathe r a case of the Muller-Lyer illusion. This problem is a very important and even fundamental issue to understand cognitive behavior in animals such as rats and pigeons.

The purpose of the present reported experiments was to determine whether or not rats perceive the Ponzo illusion, and to address the effects of the inclination and orientation of context lines on this illusion in rats. The inclination ranged from 54.6[degrees] to 125.4[degrees] (Experiments 1, 2, and 3). The orientation was either upward or downward (Experiments 1 and 3), and either rightward or leftward (Experiment 2). The theory of Nakagawa (1986, 1992a, 1993b) predicts that rats perceive the Ponzo illusion.

Experiment 1

The present experiment examined the effects of both the inclination (i.e., 54.6[degrees], 74.0[degrees], 86.4[degrees], 90.0[degrees], 93.6[degrees], 106.0[degrees], and 125.4[degrees]) and orientation (i.e., upward and downward) of the context lines on the Ponzo illusion in rats. Rats received a simultaneous discrimination of the bar length in which responses to either longer bar (or shorter bar) were rewarded with food. After completing the preliminary discrimination of the bar length, they then received a preliminary discrimination of the bars with context lines. After completing the second preliminary discrimination of the bars with context lines, they were tested with high, middle, and low context lines. The expectation according to the findings of Fujita et al. (1991, 1993) is that rats perceive the Ponzo illusion, and the magnitude of the Ponzo illusions changes with the inclination of context lines, reaching a maximum at an inclination of 54.6[degrees] and 125.4[degrees].

Method

Subjects

Sixteen experimentally naive male Sprague-Dawley rats were used. They were about 210 days old with an initial average body weight of 513 g. Animals were handled for 5 mm a day for 14 days and were maintained on a daily 2-hr feeding schedule prior to the experiment. The amount of food in the daily ration was gradually reduced until the body weight of each animal reached 80% of the baseline weight at the start of the experiment. Water was always available for animals in their individual home cages. Animals were maintained on a 4:20-hr light:dark cycle, with lights off at 8:30 a.m. Experimental sessions took place during the light phase of the cycle.

Apparatus

A Skinner box (15 cm high, 25 cm wide, and 15 cm long) was used in magazine training and lever-press training, It contained a square display screen with sides of 5 cm, which were 5 cm above the floor, and one lever beside the screen, which was a 5-cm x 3-cm rectangle and 5 cm above floor. There was a food tray on the opposite side of the lever, into which a milk pellet was delivered from a feeder when animals pressed the lever. An automatic T maze was used (Figure 1; see also Nakagawa, 1999d). The apparatus was lit throughout the experiment by a 10-W fluorescent lamp suspended 40 cm above the top of the choice chamber. The apparatus consisted of a runway (30 cm high, 12 cm in wide, and 45 cm long) with a start box (30 cm high, 12 cm wide, and 25 cm long) and a choice chamber (30 cm high, 56 cm wide, and 15 cm long). The walls of the apparatus were medium-gray Plexiglas and the ceiling was clear Plexiglas. The start box had a food tray in the center of the end wall, into which a milk pellet was delivered from a feeder when animals made a correct response. All stimuli were presented on these screens by means of a computer monitor (Sharp Hi-Vision 32C-HD90). The computer monitor was centrally located 9 cm behind the center screen and 10 cm behind the two side screens at their outer edges (the difference being due to the slight convex curvature of the face of the monitor). The choice chamber contained three display screens, each 12 cm square, which were 10 cm above the floor and 5 cm apart from edge to edge. There were two response levers in the choice chamber, each 4 cm square and 9 cm above the floor. These were located below the center of the two side screens. A guillotine door opened and closed automatically to control access to the start box. Whenever a rat interrupted a photobeam at the exit of the start box, which was located 3 cm from the guillotine door, stimuli were rear-projected automatically onto the screens. The rat was then allowed to approach and press a response lever, whenever it had to return to th e start box. As it approached it interrupted another photobeam 5 cm from the end wall of the start box, and the guillotine door closed automatically behind the rat. After 10 sec the guillotine door opened automatically for the start of the next trial. The programming of events and data collection was carried out on-line using a laboratory computer. Sound masking was provided by white noise from a blower fan (50db).

Stimuli

Black graphic patterns on white background were used rear-projected onto the side screens and medium-gray stimulus was rear-projected onto the center screen by means of the computer monitor. Pattern sizes are given below in terms of the number of graphic dots, or pixels, where appropriate, as well as the actual lengths on the computer monitor in millimeters.

Training stimuli. Discriminative stimuli in Phase 1 were rear-projected on to the side screens by means of the computer monitor. When animals pressed a response lever, the discriminative stimuli disappeared. A 6.4-mm (20 pixels) long and 1.1-mm (3 pixels) thick horizontal bar and a 3.2mm (10 pixels) long and 1.1-mm (3 pixels) thick horizontal bar were used and were presented at the center of the side screens for preliminary discrimination of the bar length in Phase 1. For preliminary discrimination of the bar length with context lines in Phase 2, long horizontal bars (6.4 mm long and 1.1 mm thick) and short horizontal bars (3.2 mm long and 1.1 mm thick) with the inclination of the context lines being either 54.6[degrees], 74.0[degrees], or 93.6[degrees] were used. These stimuli were presented at the center of the side screens. The context lines were .6 mm (2 pixels) thick and 23.7 mm (64 pixels) long vertically.

Test stimuli. Examples of the stimulus patterns used in the Phase 3 test are illustrated in Figure 2. All the patterns had a horizontal bar at the center of the side screen by means of the computer monitor. The bars were either 6.4 mm or 3.2 mm long and 1.1 mm thick. Two context lines appeared with the horizontal bar. The context lines were .6 mm thick and 23.7 mm long vertically. The inclination of the context line was either 54.6[degrees], 74.0[degrees], 86.4[degrees], 90.0[degrees], 93.6[degrees] 106.0[degrees], or 125.4[degrees] on the screen. These values were obtained by setting the tangent of the line to +1, +2, +4, infinite, -4, -2, and -1, in terms of pixels; that is, go one right and one up, one right and two up, and so forth. These values were chosen to optimize the smoothness of the graphics. All pairs of context lines were separated by 21.1 mm (66 pixels) at their midpoints.

The context lines appeared in one of the three vertical locations: high, middle, or low. For the middle context, the midpoints of the lines were level with the stimulus bar. For the high context lines, the midpoints of the lines were 7.4 mm (20 pixels) higher than the bar. For the low context lines, the midpoints were 7.4 mm lower than the bar (see Figure 2). The patterns employed as test stimuli were the same as those in Fujita et al. (1993) besides that bar lengths were limited to 6.4 mm long and 3.2 mm long.

Procedure

Magazine training and shaping of lever press. All animals received magazine training and lever-press training in the Skinner box for 5 days prior to the beginning of pretraining. On the last day all animals pressed the lever at least 50 times for 30 min a day.

Pretraining. After completing both magazine training and lever-press shaping, animals were given pretraining for 10 days prior to the beginning of the preliminary discrimination of the bar length phase until they pressed the lever at least 30 times per day on each side in the automatic T maze. That is, the animals were given such training that, after opening the guillotine door, they ran down the runway, pressed a response lever, and returned to the start box. After completing pretraining, all animals returned to the start box in less than 2 s after pressing a response lever. A medium-gray stimulus was rear-projected onto the screen during shaping and onto each of three screens during pretraining.

Training. A trial in this experiment is defined as a response-stimulus sequence, beginning when animals leave the start box after opening the guillotine door and continuing as they run down the runway, press a response lever, and return to the start box.

Phase 1: Preliminary discrimination of bar length. The stimuli were horizontal bars without context lines. The bars were short (3.2 mm) and long (6.4 mm). Animals were initially trained on the bar length discrimination task for 24 trials a day. A noncorrection training method was used. The stimuli disappeared when the animals pressed an incorrect lever, they were allowed to return to a correct response lever and press it. Lever presses at the "long" bar were correct for half of the animals, whereas lever presses at the "short" bar were correct for the remaining animals. Training continued until a criterion had been reached of 20 correct trials out of a possible 24 over 2 successive days. The position of the positive stimulus followed four predetermined random sequences. All animals were given two 45-mg milk pellets accompanied by a click of the feeder when they made a correct response. The programmed intertrial interval was 10 sec.

Phase 2: Preliminary discrimination of bar length with context lines. After completing Phase 1 training, animals were trained on three discriminations of bar length with context lines of 54.6[degrees], 74.0[degrees] and 93.6[degrees] for 24 trials a day with the noncorrection method: They were given eight trials on discrimination of bar length with inclination of 54.6[degrees], eight trials on discrimination of bar length with inclination of 74.0[degrees], and eight trials on discrimination of bar length with inclination of 93.6[degrees] a day. The context lines were the same on the two side screens. The bars were short (3.2mm) and long (6.4mm). Training continued until the same criterion as that in Phase 1 had been reached. Other aspects of the procedure were the same as those in Phase 1.

Phase 3: Test with high, middle, and low context lines. After completing Phase 2 training, the animals were tested 28 times a day for 3 successive days. The animals were required to judge either long bar or short bar between the high and low context lines (H>L condition), between the middle and low context lines (M>L condition), between the high and middle context lines (H>M condition), and between the 6.4-mm bar and the 3.2-mm one in the middle position (bar length discrimination condition), at each inclination of 54.6[degrees], 74.0[degrees], 86.4[degrees], 90.0[degrees], 93.6[degrees], 106.0[degrees], and 125.4[degrees] once per day at random. The two bars were equal lengths, 6.4 mm on the three conditions of the H>L, the M>L, and the H>M. The context lines were the same on the two side screens. For examples, the animals trained to choose the long bar were required to judge long between the high and low context lines (H>L condition) at an inclination of 54.6[degrees] with the 6.4-mm bar, to judge long betw een the middle and low context lines (M>L condition) at an inclination of 54.6[degrees] with the 6.4-mm bar, to judge long the high and middle context lines (H>M condition) at an inclination of 54.6[degrees] with 6.4-mm bar, or to discriminate between the 6.3mm bar and the 3.2-mm one in the middle position (discrimination condition) at an inclination of 54.6[degrees] at random as well as at other inclinations. By contrast, the animals trained to choose the short bar were required to judge short between the high and low context lines (H>L condition), between the middle and low context lines (M>L condition), and between the high and middle context lines (H>M condition) at an inclination of 54.6[degrees] with the 6.4-mm bar, and to discriminate between the 6.4-mm bar and the 3.2-mm bar in the middle position (discrimination condition) at an inclination of 54.6[degrees]. On test trials, responses were reinforced regardless of the location of the lever press, "long" or "short." Other aspects of the procedure were the same as those in Phase 1.

Results

Phase 1 and Phase 2 training

The rats mastered Phase 1 in 106.25 mean days (SD = 1.64), and mastered Phase 2 in 176.90 mean days (SD = 2.61).

Phase 3 test

The tendency to choose the high context stimulus in the H>L condition, the middle context stimulus in the M>L condition, and the high context stimulus in the H>L condition as a function of inclination is illustrated in Figure 3. Each data point represents the average of the percentage of long responses for the animals trained long S+ (positive stimulus) and the percentage of long response for the animals trained short S+, which is (100 -- the percent short response). Percentages of the animals that judged the high location bar longer than the low location one decreased as a function of inclination. Percentages of the animals that judged the middle location bar longer than the low location one decreased as a function of inclination. Percentages of the animals that judged the high location bar longer than the middle location one also decreased as a function of inclination. Accuracy of discrimination performance on the 6.4-mm bar -- 3.2-mm bar length discrimination task was in the 85.5%-70% range. The animals ju dged the high location bar longer than the low location bar, the middle location bar longer than the low location bar, and the high location bar longer than the middle location bar at both an inclination of 54.6[degrees] and 74.0[degrees], whereas they judged the low location bar longer than the high location bar, the low location bar longer than the middle location bar, and the middle location bar longer than the high location bar at both an inclination of 106.0[degrees] and 125.4[degrees]. The animals' performance fell into chance level of 50% - 60% at an inclination of 90.0[degrees] under each condition of the H>L, the M>L, and the H>M.

An analysis of variance using direction of context lines (upward vs. downward) and inclination (54.6[degrees] vs. 74.0[degrees] vs. 86.4[degrees]) with the repeated measure on two factors was performed on the number of responses that the animals judged the high location bar longer than the low location bar in Phase 3, which revealed a significant main effect of direction, [chi square](1) = 20.03, p < .001; a significant main effect of inclination, [chi square](2) = 240.92, p <.001; and a significant interaction, [chi square](2) = 68.62, p < .001.

A two-way analysis of variance with the repeated measure on two factors was performed on the number of responses that the animals judged the middle location bar longer than the low location bar, which revealed a significant main effect of direction, [chi square](1) = 199.92, p < .001; a significant main effect of inclination, [chi square](1) = 311.13, p < .001, and a significant interaction, [chi square](1) = 37.51, p < .001. When inclination was 54.6[degrees], there was no significant difference in the number of responses that the animals judged the middle location bar longer than the low location bar between the upward and the downward, [chi square](1) < 1. At an inclination of 74.0[degrees], the number of responses that the animals judged the middle location bar longer than the low location bar of the downward was higher than that of the upward, but this difference failed to reach significance, [chi square](1) = 2.33. At an inclination of 86.4[degrees], the number of responses that the animals judged the m iddle location bar longer than the low location bar of the downward was significantly higher than that of the upward, [chi square](1) = 5.32, p < .025.

A two-way analysis of variance with the repeated measure on two factors performed on the number of responses that the animals judged the high location bar longer than the middle location bar revealed a significant main effect of direction, [chi square](1) = 80.23, p < .001; a significant main effect of inclination, [chi square](2) = 546.42, p < .001; and a significant interaction, [chi square](2) = 465.91, p < .001. The number of responses that the animals judged the high location bar longer than the middle location bar of the downward was significantly higher than that of the upward at inclinations of both 74.0[degrees], [chi square](1) - 13.50, p < .001; and 86.4[degrees], [chi square](1) = 6.01, p < .02, but not at an inclination of 54.6[degrees], [chi square](1) = 1.98.

Discussion

The results of Experiment 1 made it clear that rats judged the high location bar longer than the low location one, the middle location bar longer than the low location one, and the high location bar longer than the middle location one in each inclination of context lines. These results indicated that the bar location made significant influence on rats' long-short judgment in each inclination of context lines. Thus, these results demonstrated that rats saw the Ponzo illusion.

Direction of context lines made significant influence on both length judgment between the middle and low location bar and length judgment between the high and middle location bar at an inclination of either 74.0[degrees] or 86.4[degrees] besides at an inclination of 54.6[degrees], but not on length judgment between the high and low location bar. These results suggested that the direction of context lines was one crucial factor for rats' Ponzo illusion, and that the downward condition of context lines facilitated rats' Ponzo illusion. These results indicated that when displays were rotated, the effect of the Ponzo illusion was reduced.

Inclination of context lines also made significant influence on length judgment under each condition of the H>L, the M>L, and the H>M. From Figure 3, as the context lines became more vertical, the effect of the Ponzo illusion was reduced, especially, under the upward conditions. This result indicated that when displays were rotated, the Ponzo illusion did reduce. These results made it clear that rats' seeing the Ponzo illusion was a perspective illusion. These results are in line with those of Fujita et al. (1993) in pigeons. The animals' performances fell into chance level of 50%-60% at an inclination of 90.0[degrees] under each condition of the H>L, the M>L, and the H>M. This result indicated that as the context lines became more vertical, the Ponzo illusion was reduced. These results suggested that inclination also was one crucial factor for rats' Ponzo illusion.

Experiment 2

The results of Experiment 1 indicated that rats saw the Ponzo illusion. Furthermore, the results made it clear that both direction and inclination of context lines with horizontal bar were crucial factor for rats' Ponzo illusion. A specific question, however, remains. Do rats see the Ponzo illusion when a pattern of stimuli is rotated 90[degrees] to either rightward or leftward? The present experiment was conducted to determine whether or not rats saw the Ponzo illusion when the bar was vertical and the direction of context lines was either rightward or leftward.

Method

Subjects

Twenty four experimentally naive male Sprague-Dawley rats were used. They were about 240 days old with an initial average body weight of 564 g. All details of feeding schedule and handling were the same as those in Experiment 1. Rats were maintained on a 6:18-hr light:dark cycle, with lights off at 9:00 a.m.

Apparatus

The apparatus was the same as that in Experiment 1.

Stimuli

The stimuli were the same as those in Experiment 1 except they were rotated 90[degrees] rightward or leftward. Examples of stimuli pattern were illustrated in Figure 4.

Procedure

All details of magazine training, shaping of lever pressing, and pretraining were the same as those in Experiment 1.

Phase 1: Preliminary discrimination of bar length. The stimuli were vertical bars without context lines. The bars were short (3.2 mm) and long (6.4 mm). Animals were initially trained on a bar length discrimination task for 24 trials a day. Lever presses at the long bar (6.4 mm) were correct for half of the animals, whereas lever presses at the short bar (3.2 mm) were correct for the remaining animals. Other aspects of the procedure were the same as those in Phase 1 of Experiment 1.

Phase 2: Preliminary discrimination of bar length with context lines. After completing Phase 1 training, animals were trained on three discriminations of bar length with context lines of 54.6[degrees], 74.0[degrees], and 93.6[degrees] for 24 trials a day. Other aspects of the procedure were the same as those in Phase 2 of Experiment 1.

Phase 3: Test with right, middle, and left context lines. After completing Phase 2 training, the animals were tested 28 times a day for 3 successive days. In Phase 3, the animals were required to judge either long bar (6.4 mm) or short bar (3.2 mm) between the right and left location, between the middle and left location, between the right and middle location, and between the 6.4-mm bar and the 3.2-mm bar in the middle position, in each inclination of 54.6[degrees], 74.0[degrees], 86.4[degrees], 90.0[degrees], 93.6[degrees], 106.0[degrees], and 125.4[degrees] once per day at random. Other aspects of the procedure were the same as those in Phase 3 of Experiment 1.

Phase 1 and Phase 2 Training

The rats mastered Phase 1 in 114.71 mean days (SD = 2.89) and Phase 2 in 200.42 mean days (SD = 2.61).

Phase 3 Test

The tendency to choose the high context stimulus in the R>L condition, the middle context stimulus in the M>L condition, and the high context stimulus in the R>L condition as a function of inclination is illustrated in Figure 5. Each data point represents the average of the percentage of long responses for the animals trained long S+ (positive stimulus) and the percentage of long responses for the animals trained short S+, which is (100 -- the percent short response). Percentages of the animals that judged the right location bar longer than the left location one decreased as a function of inclination. Percentages of the animals that judged the middle location bar longer than the left location one decreased as a function of inclination. Percentages of the animals that judged the right location bar longer than the middle location one also decreased as a function of inclination. Accuracy of discrimination performance on the 6.4-mm bar -- 3.2-mm bar length discrimination task was in the 90%-64% range. The animal s judged the right location bar longer than the left location bar at both an inclination of 54.6[degrees] and 74.0[degrees], the middle location bar longer than the left location bar at an inclination of 74.0[degrees], and the right location bar longer than the middle location bar at both an inclination of 54.6[degrees] and 74.0[degrees], whereas they judged the left location bar longer than the right location bar, the left location bar longer than the middle location bar, and the middle location bar longer than the right location bar at both an inclination of 106.0[degrees] and 125.4[degrees]. The animals' performance fell into chance level of 50%-26% at an inclination of 90.0[degrees] under each condition of the R>L, the M>L, and the R>M.

A two-way analysis of variance using direction of context lines (rightward vs. leftward) and inclination (54.6[degrees] vs. 74.0[degrees] vs. 86.4[degrees]) with the repeated measure on two factors was performed on the number of responses that the animals judged the right location bar longer than the left location bar in Phase 3, which revealed a significant main effect of direction, [chi square] = 321.20, p < .001; a significant main effect of inclination, [chi square](2) = 160.97, p < .001, and a significant interaction, [chi square](2) = 262.30, p < .001. When inclination was 54.6[degrees], the number of responses that the animals judged the right location bar longer than the left location bar of the leftward was significantly higher than that of the rightward, [chi square](1) = 23.56, p < .001. At an inclination of 74.0[degrees], the number of responses that the animals judged the right location bar longer than the left location bar of the leftward was also significantly h igher than that of the rightward, [chi square](1) = 21.79, p < .001. But at an inclination of 86.4[degrees], there was no significant difference in the number of responses that the animals judged the right location bar longer than the left location bar between the leftward and the rightward, [chi square](1) < 1.

A two-way analysis of variance with the repeated measure on two factors on the number of responses that the animals judged the middle location bar longer than the left location bar revealed a significant main effect of direction, [chi square](1) = 270.19, p < .001; a significant main effect of inclination, [chi square](2) = 384.33, p < .001; and a significant interaction, [chi square](2) = 13.42, p < .001. When inclination was 54.6[degrees], the number of responses that the animals judged the middle location bar longer than the left location bar of the leftward was significantly less than that of the rightward, [chi square](1) = 9.18, p < .005. At an inclination of 86.4[degrees], the number of responses that the animals judged the middle location bar longer than the left location bar of the leftward was lower than that of the rightward, [chi square](1) = 11.25, p < .001. And there was no significant difference in the number of responses that the animals judged the middle location bar longer than the left loca tion bar between the leftward and the rightward at an inclination of 74.0[degrees], but this difference just failed to reach significance, [chi square](1) = 3.00, .05 < p < .10.

A two-way analysis of variance with the repeated measure on two factors on the number of responses that the animals judged the right location bar longer than the middle location bar revealed a significant main effect of direction, [chi square](1) = 16.77, p < .001, a significant main effect of inclination, [chi square](2) = 70.29, p < .001, and a significant interaction, [chi square](2) = 8.90, p < .005. When inclination was 86.4[degrees], the number of responses that the animals judged the right location bar longer than the middle location bar of the rightward was higher than that of the leftward, but this difference just failed to reach significance, [chi square](1) = 2.86, .05 < p < .10.

Discussion

The results of Experiment 2 indicated that rats saw the Ponzo illusion when a pattern of stimuli was rotated 90[degrees] to either leftward or rightward. That is, on the whole, rats judged the right location bar longer than the left location one, the middle location bar longer than the left location one, and the right location bar longer than the middle location one under the rightward condition, but not under the leftward condition.

The magnitude of the Ponzo illusion in rats changed with the inclination of context lines. This result was in line with those of Experiment 1 and Fujita et al. (1993) in pigeons.

Both direction and inclination of context lines made significant influence on rats' Ponzo illusion as well as in Experiment 1. Thus, these results suggested that direction and inclination of context lines were crucial factors for rats' Ponzo illusion in both leftward and rightward conditions.

Animals' performances in the three conditions of the R>L, the M>L, and the R>M fell into the chance level of 28%-60% at an inclination of 86.4[degrees], 90[degrees], and 93.6[degrees]. These results suggested that the animals did not see the Ponzo illusion at inclinations of 86.4[degrees], 90.0[degrees], and 93.6[degrees]. That is, when the context lines became more horizontal, the effect of the Ponzo illusion was reduced under both the rightward and the leftward conditions.

Both percentages of the animals that judged the right location bar longer than the left location bar (47%) and percentages of the animals that judged the middle location bar longer than the left location bar (31%) at an inclination of 125.4[degrees] were higher than those (32% and 12.5%) at an inclination of 106.0[degrees]. Percentages of the animals that judged the middle location bar longer than the left location bar at an inclination of 54.6[degrees] were 56%. These results were not in line with the corresponding results in Experiment 1. These results suggested that the animals did not see the Ponzo illusion in both the R>L and the M>L conditions at an inclination of 125.4[degrees] and in the M>L condition at an inclination of 54.6[degrees]. These results were not consistent with those in Experiment 1. These results made it clear that when displays were rotated, the effect of the Ponzo illusion did reduce. That is, these results indicated that rats' seeing the Ponzo illusion was a perspective illusion.

Comparison between Figures 3 and 5 suggested that the animals saw the Ponzo illusion when the bar was horizontal and the direction of context lines was either upward or downward more readily than when the bar was vertical and the direction of context lines was either rightward or leftward. These results indicated that when the displays were rotated, the effect of the Ponzo illusion did reduce.

Experiment 3

The results of Experiments 1 and 2 demonstrated that rats saw the Ponzo illusion, that direction and inclination of context lines were crucial factors for rats' Ponzo illusion, and that the effect of the Ponzo illusion, however, reduced when the displays were rotated. Thus, the results of both Experiments 1 and 2 indicated that rats' seeing the Ponzo illusion was a perspective illusion. A specific question, however, remains. Do the pattern perception processes of humans and animals such as rats and pigeons exhibit similar properties? The present experiment was conducted to investigate the question of whether or not the pattern perception processes (i.e., Ponzo illusion) of humans and rats do exhibit similar properties. To investigate this problem, we needed to use the same pattern of stimuli in both humans and rats. Thus, the present experiment was conducted under the same condition as in Experiment 1 using students as subjects.

Method

Subjects

Nine experimentally naive students (5 female and 4 male) were used. They were 21 years old. They were given an instruction prior to Phase 1 training: "Say the side (e.g., right or left) that you perceive the "longer" one out of two stimuli displayed on TV." After being given this instruction, they were trained for three trials using practice stimuli in a laboratory the same size and light as those in the rats' laboratory.

Apparatus

The apparatus was the same laboratory computer and computer monitor as those in Experiment 1.

Stimuli

The stimuli were the same as those in Experiment 1.

Procedure

Phase 1: Preliminary discrimination of bar length. The stimuli were horizontal bars without context lines. The bars were the short (3.2 mm) and long (6.4 mm). Subjects were initially trained on a bar length discrimination to criterion which subjects made 24 successive correct responses. Long bar was correct for 5 subjects, whereas short bar was correct for the remaining subjects. The position of the positive stimulus was presented at random. The programmed intertrial interval was 10 sec.

Phase 2: Preliminary discrimination of bar length with context lines. After completing Phase 1 training, subjects were trained on three discriminations of bar length with context lines of 54.6[degrees], 74.0[degrees], and 93.6[degrees] to criterion. The criterion was the same as that in Phase 1. Subjects were given eight trials on the discrimination of bar length with inclination of 54.6[degrees], eight trials on the discrimination of bar length with inclination of 74.0[degrees], and eight trials on the discrimination of bar length with inclination of 93.6[degrees] in one session. Other aspects of the procedure were the same as those in Phase 1.

Phase 3: Test with high, middle, and low context lines. After completing Phase 2 training, subjects were required to judge either long bar or short bar between the high and low context lines, between the middle and low context lines, between the high and middle context lines, and between the 6.4-mm bar and the 3.2-mm bar in the middle position, in each inclination of 54.6[degrees], 74.0[degrees], 86.4[degrees], 90.0[degrees], 93.6[degrees], 106.0[degrees], and 125.4[degrees] for once in one session at random for three sessions. Responses were not reinforced in all three phases. Other aspects of the procedure were the same as those in Phase 3 in Experiment 1.

Results

Phases 1 and 2 Training

Subjects mastered Phase 1 in 24 mean trials (SD = 0.00) and Phase 2 in 24 mean trials (SD = 0.00).

Phase 3 Test

The tendency to choose the high context stimulus in the H>L condition, the middle context stimulus in the M>L condition, and the high context stimulus in the H>L condition as a function of inclination is illustrated in Figure 6. Each data point represents the average of the percentage of long responses for the students trained long S+ (positive stimulus) and the percentage of long responses for the students trained short S+, which is (100 - the percentage of short responses). Percentages of the students that judged the high location bar longer than the low location one decreased as a function of inclination. Percentages of the students that judged the middle location bar longer than the low location one decreased as a function of inclination. Percentages of the students that judged the high location bar longer than the middle location one also decreased as a function of inclination. Accuracy of discrimination performance on the 6.4mm bar -- 3.2mm bar length discrimination task was in the 78% - 56% range. The students judged the high location bar longer than the low location bar, the middle location bar longer than the low location bar, and the high location bar longer than the middle location bar at both an inclination of 54.6[degrees] and 74.0[degrees], whereas they judged the low location bar longer than the high location bar at an inclination of 106.0[degrees], the low location bar longer than the middle location bar and the middle location bar longer than the high location bar at both an inclination of 106.0[degrees] and 125.4[degrees]. The students' performances fell into chance level of 30% - 59% at an inclination of 90.00 and 93.60 under each condition of the H>L, the M>L, and the H>M without the H>M condition at an inclination of 90.0[degrees].

A two-way analysis of variance using direction of context lines (upward vs. downward) and inclination (54.60 vs. 74.0[degrees] vs. 86.4[degrees]) with the repeated measure on two factors was performed on the number of responses that students judged the high location bar longer than the low location bar in Phase 3, which revealed a significant main effect of direction, [chi square](1) = 728.49, p < .001, a significant main effect of inclination, [chi square](2) = 392.28, p < .001, and a significant interaction, [chi square](2) = 564.43, p < .001. When inclination was 54.60, the number of responses that students judged the high location bar longer than the low location bar of the downward was significantly higher than that of the upward, [chi square](1) = 12.27, p < .001. At an inclination of 74.00, the number of responses that students judged the high location bar longer than the low location bar of the downward was also significantly higher than that of the upward, [chi square](1) = 12.26, p < .001. But there was no significant difference in accuracy between the upward and the downward at an inclination of 86.40, [chi square](1) < 1.

A two-way analysis of variance with the repeated measure on two factors on the number of responses that students judged the middle location bar longer than the low location bar revealed a near significant main effect of direction, [chi square] (1) = 3.13, .05 < p < .10, a significant main effect of inclination, [chi square](2) = 148.61, p < .001, and a significant interaction, [chi square](2) = 330.32, p < .001. When inclination was 54.6[degrees] the number of responses that students judged the middle location bar longer than the low location bar of the downward was higher than that of the upward, [chi square](1) = 3.86, p < .05. At an inclination 86.4[degrees], the number of responses that students judged the middle location bar longer than the low location bar of the upward was higher than that of the downward, but this difference just failed to reach significance, [chi square](1) = 3.00, .05 > p < .10. But there was no significant difference in the number of responses that students judged the middle locati on bar longer than the low location bar between the upward and the downward at an inclination of 74.00, [chi square](1) < 1.

A two-way analysis of variance with the repeated measure on two factors on the number of responses that students judged the high location bar longer than the middle location bar between the high and middle location bar revealed a significant main effect, [chi square] (1) = 47.64, p < .001, a significant main effect of inclination, [chi square](2) = 482.91, p < .001, and a significant interaction, [chi square](1) = 95.30, p < .001. When an inclination was 54.6[degrees], the number of responses that students judged the high location bar longer than the middle location bar of upward was higher than that of the downward, but this difference just failed reach significance, [chi square](1) = 2.85, .05 < p < .10. .10.

The results of Experiments 1, 2, and 3 suggest that the ratio of difference in distance between bars and context was a very crucial factor for rats' and humans' Ponzo illusion. The ratios used in Experiments 1, 2, and 3 were as follows: 0.14 (high vs. low at an inclination of 54.60 and 125.4[degrees]), 0.25 (high vs. middle at an inclination of 54.60 and 125.4[degrees]), 0.40 (high vs. low at an inclination of 74.0[degrees] and 106.0[degrees]), 0.50 (high vs. middle at an inclination of 74.0[degrees] and 106.0[degrees], 0.57 (middle vs. low at an inclination of 54.6[degrees] and 125.4[degrees]), 0.60 (high vs. low at an inclination of 86.4[degrees] and 93.6[degrees]), 0.75 (high vs. middle at an inclination of 86.4[degrees] and 93.6[degrees]), 0.80 (middle vs. low at an inclination of 74.0[degrees] 86.4[degrees]; high vs. middle at an inclination of 93.6[degrees], and 106.0[degrees]), and 1.00 (high vs. low, middle vs. low, and high vs. middle at an inclination of 90.0[degrees]). So, in order to examine the m agnitude of influence which the ratio of difference in distance between bars and context made on rats' and humans' judgments, percentages of the subjects that judged the high location bar longer than the low location one, that judged the middle location bar longer than the low location one, and that judged the high location bar longer than the middle location one were calculated on every ratio. The percentages are illustrated in Figure 7. An ANOVA using experiment (Experiment 1 vs. Experiment 2 vs. Experiment 3) and ratio (0.14 vs. 0.25 vs. 0.40 vs. 0.50 vs. 0.57 vs. 0.60 vs. 0.75 vs. 0.80) revealed a significant main effect of ratio, F(7, 23) = 7.38, p < .01 and a significant interaction, F(14, 23) = 4.30, p < .01, but no significant main effect of Experiment, F(2, 23) = 2.69. This result indicated that the pattern perception processes (i.e., Ponzo illusion) of rats and humans exhibited similar properties. That is, the ratio of difference in distance between bars and context was a very crucial factor for rat s' and humans' Ponzo illusion. Inspection of Figure 7 suggested that the ratios of 0.57 in Experiment 2, 0.60 in Experiments 2 and 3, and 0.75 in Experiments 2 and 3, and 1.00 in Experiments 1, 2 , and 3 hindered the Ponzo illusion more than other ratios (i.e., 0.14, 0.25, 0.40, 0.50, and 0.80) for animals and humans, and decreased accuracy of judgment more than other ratios (i.e., 0.14, 0.25, 0.40, 0.50, and 0.80) for rats and humans. This inspection of Figure 7 indicated that, when the displays were rotated, the effect of the Ponzo illusion reduced, especially, as the context lines became more horizontal at an inclination of 86.4[degrees] and 93.6[degrees] in Experiment 2.

Discussion

The results of Experiment 3 made it clear that humans judged the high location bar longer than the low location one, the middle location bar longer than the low location one, and the high location bar longer than the middle location one as well as did rats, with exception of the inclination of 90.0[degrees].

Direction and inclination of context lines made significant influence on humans' Ponzo illusion. Thus, these results suggested that direction and inclination of context lines were crucial factors for humans' Ponzo illusion as well as for rats' Ponzo illusion.

The magnitude of the Ponzo illusion in humans changed with an inclination of 54.6[degrees], 74.0[degrees], and 125.4[degrees] (see Figure 6). The results were in line with those of Experiments 1 and 2 in rats and Fujita et al. (1993) in pigeons.

Students judged the high location bar longer than the middle location bar at an inclination of 90.0[degrees]. This result was not in line with results in Experiments 1 and 2, in which choices of the animals were at random at an inclination of 90.0[degrees].

Inspection of Figure 7 indicates that the ratio of difference in distance between bars and context was a very important factor for rats' and humans' Ponzo illusion.

General Discussion

The present study was conducted to demonstrate that rats responded to configurations of stimuli to provide strong evidence for the theory of Nakagawa (1986, 1992a, 1993b) on stimulus classes formation. In Experiment 1 rats showed a systematic distortion in bar-length perception according to inclination of context lines. The magnitude of the Ponzo illusion in rats changed with the inclination of context lines, reaching a maximum at an inclination of 54.6[degrees], 74.0[degrees], and 125.4[degrees] (see Figure 3). Direction of context lines made a significant influence on bar-length perception at either of two inclinations, 54.6[degrees] and 86.4[degrees], with the high location and middle location bar or at inclination of 86.4[degrees] with the middle location and low location bar situation. Experiment 2 replicated the results of Experiment 1. But there were significant differences in bar-length perception between the rightward and leftward of context lines at either of two inclinations, 54.6[degrees] and 74.0 [degrees], with the right location and left location bar, or at two inclinations of 54.6[degrees] and 86.4[degrees] with the middle location and left location bar situation. In Experiment 3, humans showed a systematic distortion in bar-length perception according to the inclination of context lines as well as in Experiments 1 and 2 in rats. That is, the magnitude of the Ponzo illusion in humans changed with the inclination of context lines, reaching a maximum at an inclination of 54.6[degrees], 74.0[degrees] and 125.4[degrees] (see Figure 6). And direction of context lines made a significant influence on bar-length perception at only two inclinations of 56.4[degrees] and 74.0[degrees] with the high location and low location bar situation. Thus, the findings of the three present experiments offer strong empirical evidence that the animals saw the Ponzo illusion, and that the pattern perception (i.e., Ponzo illusion) of humans and animals had similar properties, in which both the inclination of context lines an d the direction of displays made significant effect on the Ponzo illusion in either rats or humans.. These findings were in line with the expectation from the theory of Nakagawa (1986, 1992a, 1993b).

Rats showed a consistent tendency to report bar length longer more often when the inclination of context lines was small, say, when the bar was near the apex of the converging context lines, in Experiment 1. Figure 7 showed clearly the effect of different ratios of bar length to gap length (i.e., effect of gap length). This effect was that as the size of the gap decreased then the likelihood of a rat responding the bar as "long" was increased. Alternatively, as gap length was decreased then the likelihood of producing fusion between the ends of the bar and the context lines was increased. Results of Experiments 2 and 3 showed this effect, but Experiment 1 did not. That is, under the downward and upward conditions in Experiment 1, as gap length was decreased then the likelihood of a rat responding the bar as "long" was increased. By contrast, when a display was rotated to either the rightward or leftward, as gap length was decreased then the likelihood of producing fusion between the ends of the bar and the co ntext lines was increased as in Experiment 2 in rats. Thus, under the downward and the upward condition as in Experiment 1, rats were truly seeing a longer line. These findings were in line with the findings of Fujita et al. (1991, 1993) in pigeons. These findings of Experiment 1 suggested that the distance between the stimulus bar and the context lines was an important determinant of rats' Ponzo illusion as well as in pigeons' Ponzo illusion. Fisher (1969, 1973) suggested that the magnitude of illusion was determined by the gap between the stimulus bar and context lines. The present results were approximately consistent with Fisher's account (1969, 1973), but for a more complete test it would be necessary to test the rats' performances with variations in the ratio of bar to gap independent of the type and the inclination of context lines.

The magnitude of the illusion did differ in directions whether the context lines converged upward or downward (or rightward or leftward) in Experiments 1 and 2 in rats. For example, on the high-low location bar at two inclinations of 74.0[degrees] and 86.4[degrees], upward figures were more powerful in inducing the illusion than downward figures in Experiment 1, whereas on the middle-left location bar at two inclinations of context lines of 54.6[degrees] and 86.40[degrees], leftward figures were more powerful in inducing the illusion than rightward figures in Experiment 2. That is, these findings indicated that when the display was rotated, the effect of the Ponzo illusion reduced in rats. These findings made it clear that the effect of the Ponzo illusion in rats was a perspective illusion but not the Muller-Lyer illusion. These findings are not in line with the findings of Fujita et al. (1991, 1993) in pigeons. In general for humans, upward figures are a little more powerful in inducing the illusion than are horizontal or downward figures. In Experiment 3 of the present study also, the magnitude of the illusion did differ as a function of whether the context lines converged upward or downward. Students judged the high location bar longer than the middle location bar at an inclination of 90.0[degrees]. This result was not in line with results in Experiments 1 and 2, in which choices of the animals were at random at an inclination of 90.0[degrees]. Furthermore, effects of rotation of displays were significant at an inclination of 54.6[degrees], in students, whereas they were not significant in rats in Experiment 1. That is, for rats in Experiment 1, direction of upward and downward displays did not affect rats' perception (i.e., Ponzo illusion) at an inclination of 54.6[degrees] whereas direction of upward and downward of displays affected students' perception at an inclination of 54.6[degrees]. These results made it clear that students' Ponzo illusion was different from rats' Ponzo illusion. This discrepancy of r esults might be due to culture and level of education in subjects (i.e., human subjects). Many experiments suggest that in humans, culture and level of education affect the magnitude of the Ponzo illusion (Brislin, 1974; Brislin & Keating, 1976; Kilbride & Leibowitz, 1975; Predebon, 1984; Pressey, 1974; Quina & Pollack, 1972; Wagner, 1977).

These findings of Experiments 1 and 2 made it clear that rats perceived a bar length on the basis not of bar length itself but configurations of stimuli.

The findings of the present experiments suggested that rats saw the Ponzo illusion, which was a perspective illusion, and that the inclination of context lines was an important determinant for rats' Ponzo illusion as well as in pigeons and humans.

The findings of the present experiments made it clear that rats responded to configurations of stimuli as well as did humans. Nakagawa (1986, 1992a, 1993b) asserted that stimuli or stimulus sets that are associated with the same outcome (e.g., food or no food) would come to be classed together, despite their perceptual dissimilarity. According to Nakagawa, rats formed associations between the discriminative stimuli with the same response assignment during overtraining on two concurrent discriminations and these associations mediated the transfer of appropriate responding when discriminations were reversed (Nakagawa, 1992a). In the case of matching- (or nonmatching)-to-sample (MTS or QES) discriminations or same-different discriminations, we had to allow rats to associate a configuration of stimuli with lever-pressing responses, and then to form associations between the configurations of stimuli with the same response assignment. For example, in a MTS task, rats learned to associate one configuration of stimul i (i.e., AAB and BBA) with pressing the left lever followed by a reward and the other configuration (i.e., BAA and ABB) with pressing the right lever followed by a reward, in which the two side letters referred to the comparison stimuli and the center letter referred to the sample stimulus. They then formed associations between the configurations of stimuli with the same response assignment and it was these configuration associations that mediated the transfer of appropriate responding to a subsequent shift problem (Nakagawa, 1993b). The basic idea of Nakagawa's proposal that a common response mediated concepts of matching and nonmatching, or sameness to or difference from subsequent shift problems assumed that the novel stimuli and novel configurations appearing in the transfer tests generated the same mediator (i.e., common response to configurations of stimuli). Thus, these findings of the present experiments provided strong evidence that rats responded to configurations of stimuli, that is, these findings of the present experiments provided strong evidence for the basic idea of Nakagawa's proposal.

[FIGURE 3 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

References

AGGLETON, J. P. (1985). One-trial object recognition by rats. Quarterly Journal of Experimental Psychology, 37B, 279-294.

ALLAN, S. E., & BLOUGH, D. S. (1989). Feature-based search asymmetries in pigeons and humans. Perception & Psychophysics, 46, 456-464.

BAYNE, K. A. L, & DAVIS, R. T. (1983). Susceptibility of rhesus monkeys (Macaca mulatta) to the Ponzo illusion. Bulletin of the Psychonomic Society 21, 476-478.

BENHAR, E., & SAMUEL, D. (1982). Visual illusions in the baboon (Papio anubis). Animal Learning & Behavior, 10, 115-118.

BLOUGH, D. S. (1982). Pigeons recognition of letters of the alphabet. Science, 218, 397-398.

BLOUGH, D. S. (1985). Discriminations of letters and random dot patterns by pigeons and humans. Journal of Experimental Psychology: Animal Behavior Processes, 11, 261-280.

BRISLIN, R. W. (1974). The Ponzo illusion: Additional cues, age, orientation, and culture. Journal of Cross Cultural Psychology, 5, 139-161.

BRISLIN, R.W., & KEATING, C. F (1976). Cultural differences in the perception of a three-dimensional Ponzo illusion. Journal of Cross Cultural Psychology, 7, 397-412.

COOK, R. G., CAVOTO, K. K., & CAVOTO, B. R. (1995). Same-different texture discrimination and concept learning in pigeons. Journal of Experimental Psychology: Animal Behavior Processes, 21, 253-260.

COOK, R. G., CAVOTO, K. K., & CAVOTO, B. R. (1996). Mechanisms of multidimensional grouping, fusion, and search in avain texture discrimination. Animal Learning & Behavior, 24, 150-167.

COOK, R. G., KATZ, J. S., & CAVOTO, B. R. (1997). Pigeon same-different concept learning with multiple stimulus classes. Journal of Experimental Psychology: Animal behavior Processes, 23, 417-433.

COOK, R. G., & WIXED, J. T. (1997). Same-different texture discrimination in pigeons: Testing competing models of discrimination and stimulus integration. Journal of Experimental Psychology: Animal Behavior Processes, 23, 401-416.

DELIUS, J. D., AMELING, M., LEA, S. E. G., & STADDON, J. E. R. (1995). Reinforcement concordance induces and maintains stimulus associations in pigeons. The Psychological Record, 45, 283-297.

DOMINGUEZ, K. E. (1954). A study of visual illusions in the monkey. Journal of Genetic Psychology, 85,105-127.

DUBE, W. V., CALLAHAN, T. D., & MCILVANE, W. J. (1993). Serial reversals of concurrent auditory discriminations in rats. The Psychological Record, 43, 429-440.

EDWARDS, C. A., JAGIELO, J. A., & ZENTALL, T. R. (1983). "Same/different" symbol use by pigeons. Animal Learning & Behavior, 11, 349-355.

EDWARDS, S. A., JAGIELO, J. A., ZENTALL, T. R., & HOGAN, D. E. (1982). Acquired equivalence and distinctiveness in matching-to-sample by pigeons: Mediation by reinforcer-specific expectancies. Journal of Experimental Psychology: Animal Behavior Processes, 8, 244-259.

FETTERMAN, J. G. (1991). Discrimination of temporal same-different relations by pigeons. In M. L. Commons, J. A. Nevin, & M. C. Davison (Eds.), Signal detection: Mechanisms, models, and applications (pp. 79-101). Hillsdale, NJ: Erlbaum.

FISHER, G. H. (1969). Towards a new explanation for the geometrical illusions: I. The properties of contours which induce illusory distortion. British Journal of Psychology, 60,179-185.

FISHER, G. H. (1973). Towards a new explanation for the geometrical illusion: II. Apparent depth or contour proximity? British Journal of Psychology, 64, 607-621.

FUJITA, K., BLOUGH, D. S., & BLOUGH, R M. (1991). Pigeons see the Ponzo illusion. Animal Learning & Behavior, 19, 283-293.

FUJITA, K., BLOUGH, D. S., & BLOUGH, R M. (1993). Effects of the inclination of context lines on perception of the Ponzo illusion by pigeons. Animal Learning & Behavior, 21, 29-34.

KILBRIDE, P. L., & LEIBOWITZ, H.W. (1975). Factors affecting the magnitude of the Ponzo perspective illusion among the Baganda. Perception & Psychophysics, 17, 543-548.

LOMBARDI, C. M., FACHINELLI, C. C., & DELIUS, J. D. (1984). Oddity of visual pattern conceptualized by pigeons. Animal Learning & Behavior, 12, 2-6.

MALOTT, R. W., & MALOTT M. K. (1970). Perception and stimulus generalization. In W. C. Stebbins (Ed.), Animal psychophysics: The design and conduct of sensory experiments (pp. 363-400). New York: Plenum.

MALOTT, R. W., MALOTT, M. K., & POKRZYWINSKI, J. (1967). The effects of outward-pointing arrowheads on the Muller-Lyer illusion in pigeons. Psychonomic Science, 9, 55-56.

MUMBY, D. G., PINEL, J. R, & WOOD, E. R. (1990). Nonrecurring items delayed nonmatching-to-sample in rats: A new paradigm for testing nonspatial working memory. Psychobiology, 18, 321-326.

NAKAGAWA, E. (1978). The effect of overtraining on discrimination learning in white rats (in Japanese). Japanese Journal of Psychology, 49, 70-77.

NAKAGAWA, E. (1986). Overtraining, extinction and shift learning in a concurrent discrimination in rats. Quarterly Journal of Experimental Psychology, 38B, 313-326.

NAKAGAWA, E. (1992a). Effects of overtraining reversal learning by rats in concurrent and single discriminations. Quarterly Journal of Experimental Psychology, 44B, 37-56.

NAKAGAWA, E. (1992b). Transfer of a matching and nonmatching concept in rats. Psychobiology, 20, 311-314.

NAKAGAWA, E. (1993a). Matching and nonmatching concept learning in rats. Psychobiology, 21, 142-150.

NAKAGAWA, E. (1993b). Relational rule learning in the rat. Psychobiology, 21, 293-298.

NAKAGAWA, E. (1998). Stimulus classes formation in concurrent discriminations in rats as a function of overtraining. The Psychological Record, 48, 537-552.

NAKAGAWA, E. (1999a). A factor affecting stimulus classes formation in concurrent discriminations in rats. The Psychological Record, 49, 117-136.

NAKAGAWA, E. (1999b). Acquired equivalence of discriminative stimuli following two concurrent discrimination learning tasks as a function of overtraining in rats. The Psychological Record, 49, 327-348.

NAKAGAWA, E. (1999c). Mechanism of stimulus classes formation in concurrent discriminations in rats. The Psychological Record, 49, 349-368.

NAKAGAWA, E. (1999d). Transfer of learning between concurrent discriminations and matching (or non-matching)-to-sample discriminations in rats. Quarterly Journal of Experimental Psychology, 51B, 125-143.

NAKAGAWA, E. (2000a). Reversal learning in conditional discriminations is not controlled by reinforcer density. The Psychological Record, 50, 117-140.

NAKAGAWA, E. (2000b). Transfer of learning between matching (or nonmatching)-to-sample and same-different discriminations. The Psychological Record, 50, 771-805.

NAKAGAWA, E. (2001). Cross-modal stimulus class formation in rats. The Psychological Record, 51, 53-66.

PREDEBON, J. (1984). Age trends in the Mueller-Lyer and Ponzo illusions. British Journal of Developmental Psychology, 3, 99-103.

PRESSEY, A. W. (1974). Age changes in the Ponzo and filled-space illusions. Perception & Psychophysics, 15, 315-319.

QUINA, K., & POLLACK, R. H. (1972). Effects of test line position and age on the magnitude of the Ponzo illusion. Perception & Psychophysics, 12, 253-256.

ROTHBLAT, L. A., & HAYES, L. L. (1987). Short-term object recognition memory in rats: Nonmatching with trial-unique junk stimuli. Behavioral Neuroscience, 101, 578-590.

SANTIAGO, H., & WRIGHT, A. A. (1984). Pigeon memory: Same/different concept learning, serial probe recognition acquisition, and probe delay effects on the serial-position function. Journal of Experimental Psychology: Animal Behavior Processes, 10, 498-512.

URCUIOLI, P. J. (1977). Transfer of oddity-from-sample performance in pigeons. Journal of the Experimental Analysis of Behavior, 27,149-155.

URCUIOLI, P J., & NEVIN, J. A. (1975). Transfer of hue matching in pigeons. Journal of the Experimental Analysis of Behavior, 24,149-155.

URCUIOLI, P. J., ZENTALL, T. R., JACKSON-SMITH, P., & STEIRN, J. N. (1989). Evidence for common coding in many-to-one matching: Retention, intertrial interference, and transfer. Journal of Experimental Psychology: Animal Behavior Processes, 15, 264-273.

VAUGHAN, W., Jr. (1988). Formation of equivalence sets in pigeons. Journal of Experimental Psychology: Animal Behavior Processes, 14, 36-42.

WAGNER, D. A. (1977). Ontogeny of the Ponzo illusion: Effects of age, schooling, and environment. International Journal of Psychology, 49, 273-279.

WASSERMAN, E. A., HUGART, J. A., & KIRKPATRICK-STEGER, K. (1995). Pigeons show same-different conceptualization after training with complex visual stimuli. Journal of Experimental Psychology: Animal Behavior Processes, 21, 248-252.

WRIGHT, A. A., SANTIAGO, H. C., SANDS, S. F., KENDRICK, D. F., & COOK, R. G. (1985). Memory processing of serial list by pigeons, monkey, and people. Science, 229, 287-289.

WRIGHT, A. A., SANTIAGO, H. C., URCUIOLI, P. J., & SANDS, S. F. (1983). Monkey and pigeon acquisition of same/different concept using pictorial stimuli. In M. L. Commons, R. J. Herrstein, & A. R. Wagner (Eds.), Quantitative analysis of behavior(Vol. 4, pp. 295-317). Cambridge, MA: Ballinger.

YOUNG, M. E., & WASSERMAN, E. A. (1997). Entropy detection by pigeons: Response to mixed visual displays after same-different discrimination training. Journal of Experimental Psychology: Animal Behavior Processes, 23, 157-170.

YOUNG, M. E., WASSERMAN, E. A., & GARNER, K. L. (1997). Effects of number of items on the pigeon's discrimination of same from different visual displays. Journal of Experimental Psychology: Animal Behavior Processes, 23, 491-501.

ZENTALL, T. R., & HOGAN, D. E. (1974). Abstract concept learning in the pigeon. Journal of Experimental Psychology, 102, 393-398.

ZENTALL, T. R., & HOGAN, D. E. (1975). Concept learning in the pigeon: Transfer to new matching and nonmatching stimuli. American Journal of Psychology, 88, 233-244.

ZENTALL, T. R., & HOGAN, D. E. (1976). Pigeons can learn identity or difference. Science, 191, 408-409.

ZENTALL, T. R., SHERBURNE, L. M., STEIRN, J. N., RANDALL, C. K., ROPER, K. L., & URCUIOLI, P. J. (1992). Common coding in pigeons: Partial versus total reversals of one-to-many conditional discriminations. Animal Learning & Behavior, 20, 373-381.

ZENTALL, T. R., STEIRN, J. N., SHERBURNE, L. M., & URCUIOLI, P. J. (1991). Common coding in pigeons assessed through partial versus total reversals of many-to-one conditional and simple discriminations. Journal of Experimental Psychology; Animal Behavior Processes, 17, 194-201.

Requests for reprints should be sent to Esho Nakagawa, Department of Psychology, Kagawa University, 1-1, Saiwai-Cho, Takamatsu, Kagawa, 760-8522, Japan. (E-mail: esho@ed.kagawa-u.ac.jp).
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Author:Nakagawa, Esho
Publication:The Psychological Record
Date:Sep 22, 2002
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