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Demonstrating habituation of a startle response to loud noise.

While classical conditioning is no doubt a standard part of most if not all introductory psychology courses, habituation is less prevalent as a topic. A search of Teaching of Psychology and others sources uncovered classroom demonstrations of classical conditioning processes, (Gibb, 1983; Kohn and Kalat, 1992; Sparrow & Fernald, 1989; Vernoy, 1987) while no examples of demonstrations of habituation were found. Most psychology students are familiar with the startle reflex, which is "a universal and phylogenetically ancient reflex," (Howard & Ford, 1992, p. 695); it is one of the innate, defensive reflexes of humans and other vertebrates that occur in response to unconditioned eliciting stimuli such as an unexpected loud noise. A startle reflex that is elicited by an unpredicted noise is referred to as an acoustic or audiogenic startle reflex, (Wilkens, Hallett, & Wess, 1986; Brown, Rothwell, Thompson, Britton, Day, & Marsden, 1991; Gluck, Mercado, & Myers, 2008). Habituation is the process by which such reflexes are modified by experience; hence, it is a basic form of learning (Bouton, 2007; Gluck et al., 2008).

A normal audiogenic startle reflex was first quantifiably studied by Jacobsen (1926), with further study by Landis and Hunt, (1936, 1937, 1939). The acoustic startle reflex consists of eye movements, especially blinking, facial grimacing, contractions of flexor muscles in the neck, trunk and elbows, with extensor muscles being activated much less often. Movements of the head and the remainder of the body are less reliably involved (Brown et al., 1991; Wilkens et al., 1986). Habituation occurred for all of these components with the exception of blinking (Wilkens et al., 1986). Howard and Ford (1992) observed considerable variation between individuals in the topography and duration of the startle reflex.

As noted by Wilkens et al., (1986) the startle reflex is subject to habituation. Typically, an unconditioned response or reflex that is elicited by an unconditioned stimulus will show habituation if the stimulus is repeated (Gluck et al., 2008). That is, measures of the response will show orderly decreases in magnitude as the stimulus is repeatedly applied. More simply put, habituation is the process by which a stimulus loses its attention-grabbing properties, i.e., its "novelty," and decreases in responsiveness to the stimulus are seen when the stimulus is presented repeatedly or for an extended period. Through the process of habituation, an organism ceases to engage in attending or other responses to the stimulus; the stimulus comes to be ignored (Bouton, 2007; Gluck et al., 2008). To illustrate habituation, the contingencies needed to elicit an acoustic startle reflex were arranged and repeated to record the habituation of the various responses.


Due to difficulties with an audience observing a person undergo a startle reflex, the demonstration to be described was conducted in another setting and digitally videotaped for later use in the classroom. Prior to any observations, protocol approval was obtained from the South Dakota State University Institutional Review Board. Four research assistants were involved, one of whom had volunteered to be videotaped and exposed to an eliciting stimulus; we initially needed to determine an effective unconditioned stimulus (US) with which to elicit the startle reflex, with the designated volunteer out of the room. We initially tested balloons being popped as suggested by Vernoy (1987), but found this event was not effective at eliciting a significant response. After some trial and error, we decided to strike a metal table with a standard weight claw hammer, which at an approximate distance of 1 m elicited a clearly observable startle reflex. A sound decibel meter allowed us to quantify the decibel level, approximately 80 dB. To produce rapid habituation, an inter-stimulus interval (ISI) of 15 s was employed.


The sole participant was a 21-year-old psychology student, who described herself as having an exaggerated startle response. She was told a loud noise would be produced behind her on a set schedule to produce a startle reflex and she was seated, facing the camera.


During the interval prior to the first stimulus event, the volunteer was observed to look somewhat uncomfortable or awkward, with eye movements and facial gestures of either boredom or uncertainty, as might be expected with a camera recording her actions and she not knowing what to do or exactly what would happen. The subject startled visibly with several muscle groups of the upper body in response to the initial stimulus presentation (i.e., striking the table with the hammer). In detail, her eyes widened and she blinked repeatedly, she displayed facial grimacing; she vocalized a brief sharp gasp-inhalation and brought one of her hands up from her lap to cover her mouth. Her breathing accelerated, she smiled nervously and looked embarrassed during the subsequent ISI. A very similar response class was elicited by the 2nd stimulus presentation. During the 3rd stimulus presentation, the degree of startle was somewhat reduced in magnitude, the vocalization was still present but no movement of the arm occurred. By the 4th stimulus presentation, the vocalization no longer occurred, and the magnitude of the startle reflex was clearly habituating. In the midst of the 5th, 6th and 7th stimulus presentations, the elicited response class consisted solely of some muscle movements of the upper body, with no changes in facial expression or widening of the eyes. Whilst the 8th stimulus presentation occurred, the magnitude of elicited muscle movements of the upper body was significantly reduced, with little movement observable at all. During the 9th and 10th stimulus presentation, the videotape shows little observable, elicited movement and the volunteer looks noticeably bored during the ISI, with just a few eye movements occurring. By the time of the 12th stimulus presentation, there was no observable muscular response to the US. The stimulus was presented for a 13th time and again no observable response occurred.

At this point in time, a 2-min pause from further US presentations and video recording was implemented; this pause was employed in hopes of observing spontaneous recovery of the habituated reflex. During this pause, the volunteer was allowed to leave the room and walk down the hallway to visit the restroom and look in the mirror to compose herself; following this break, we resumed the former procedures.

In response to the 1st stimulus presentation in this stimulus series, elicited muscle contractions of volunteer's upper body were clearly observable. These movements were greater in magnitude relative to the elicited movements seen at the end of the 1st set of stimulus presentations but also noticeably diminished compared to the elicited movements from the initial onset of stimulus presentations. No other responses were observable. The recovery in strength of a habituated response after a short period without any stimulus presentations is referred to as spontaneous recovery, (Gluck et al., 2008). During the 2nd stimulus presentation, the magnitude of the elicited movements was reduced; by the time of the 4th and 5th stimulus presentations, very little movement was observable. The 6th and a 7th stimulus presentation produced no observable response.

Initially, twelve stimulus presentations were required to produce habituation of the startle reflex; to produce habituation of the startle reflex that had undergone apparent spontaneous recovery, only six stimulus presentations were required. This time course fits with what is predicted of repeated habituation sessions. After an initial habituating experience, subsequent habituation experiences are known to occur more rapidly, with fewer stimulus presentations being required (Groves and Thompson, 1970; Thompson & Spencer, 1966).

Seven days later, another habituation session was conducted in the same setting; unbeknownst to the same volunteer as before, an extraneous auditory event was included in this session in hopes of observing dishabituation. One of the properties of habituation is that presentation of an irrelevant stimulus will result in the recovery of the habituated response to the US, termed dishabituation (Groves and Thompson, 1970; Thompson & Spencer, 1966).

Here, the same US was used as before, along with the same ISI of 15 s. Again, the volunteer was videotaped seated and facing the camera. The 1st stimulus presentation elicited notable muscle contractions of the upper body, the volunteer again vocalized a brief inhalation gasp-cry, similar to the responses observed a week prior. The 2nd stimulus presentation appeared to elicit a greater magnitude of startle reflex in terms of movements and volume of the vocalization. The 3rd and 4th stimulus presentation elicited a somewhat variable course of some apparent habituation and some increase in magnitude of response. By the 5th stimulus presentation, the magnitude of the startle reflex was noticeably decreased. During the 6th stimulus presentation, the observable response to the US was very small and during the 7th stimulus event, any response at all was difficult to observe.

Just before the 8th stimulus event, the research assistants were given an agreed upon signal (a scratch of the first author's head) whereupon a "party horn" was blown for approximately one s, followed immediately by the US. The blowing of the "party horn" was used an extraneous environmental event and was predicted to result in an increase in the response magnitude of the startle reflex (Groves and Thompson, 1970; Thompson and Spencer, 1966), and a slight increase in the amount of elicited movement was observable during the 8th US of this session, consistent with the process of dishabituation. By the time of the 12th US presentation, very little if any startle reflex was observable, which continued to be the case during a 13th and 14th US presentation.


To assess the utility of this demonstration in teaching a Learning and Conditioning course, another IRB approval was obtained before a brief survey was administered twice, each to two different sections of the same course. Section 01 (n = 57), took the survey, heard a lecture on habituation and its aspects, saw the video with narration and took the survey again. Section 02 (n = 21), which was taught at another campus approximately 50 miles away, took the survey, heard the same lecture, took the survey again and was then shown the video demonstration. The anonymous survey consisted of four questions which were intended to assess the student's self-report of their familiarity with the concepts of habituation, spontaneous recovery and dishabituation. The survey seemed to indicate that the video demonstration was more effective in addressing these concepts than a lecture with PowerPoint slides alone.


The demonstration described above was designed as a means of demonstrating habituation of an elicited unconditioned reflex due to a loud auditory event and the related processes of spontaneous recovery and dishabituation. The question most likely remaining after our demonstration is whether or not the volunteer's behavior was actual habituation or conversely, examples of response biases by the participant. To investigate whether response biases were occurring, after this participant had finished her degree requirements and had graduated, she was directly asked if she had been trying to be an ideal subject; she reported that the startle she displayed was authentic and not acting or embellishment. Sparrow and Fernald (1989) suggested that the use of an objective response measure such as the GSR makes such concerns less probable. The possibility of response bias cannot be ruled out and the fact that the responses observed in the demonstration we arranged were those of the skeletal muscles further complicates the case for a valid instance of habituation. Nevertheless, the fact that habituation was observed but also spontaneous recovery and dishabituation makes this scenario less likely. The volunteer who was videotaped was a student in the Learning and Conditioning class at the time of the demonstration; the textbook being used discussed habituation but neither spontaneous recovery nor dishabituation (Pierce and Cheney, 2004). While she still could have admittedly learned of these two latter processes on her own, being an ideal subject to the extent of acting out both spontaneous recovery and dishabituation is a bit of a reach in the opinion of this writer and presumably of most skeptics.

The video recording has been used to illustrate the process of habituation to undergraduate students in a Learning and Conditioning course and it accomplishes the intended purpose reasonably well. The video can be made available to other instructors who wish to use it, with one note of caution. The individual who was video recorded consented to and the initial IRB approval was for use in the classroom only. The video demonstration can be shared at no charge (i.e., some medium for sharing large files such as DropBox or a compact disc sent by mail) with any interested instructor for use in the classroom but cannot be posted on any public-use website where it could be copied and posted into a website such as YouTube.


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Brady J. Phelps, Lyndsay Doyle-Lunders, Amanda Harsin-Waite, Nicole Hofman and Lacy M. Knutson

South Dakota State University

Correspondence concerning this paper should be sent to Brady J. Phelps, Professor of Psychology, South Dakota State University, Scobey Hall Box 504, Brookings, South Dakota 57007, email:

Lyndsay Doyle-Lunders is now living in Clarksville, Tennessee, Amanda Harsin-Waite is now living in Pierre, South Dakota, Nicole Hofman is now at the University of South Dakota, Vermillion, South Dakota and Lacy M. Knutson is now at Developmental Behavioral Health, Inc, Colorado Springs, Colorado
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Author:Phelps, Brady J.; Doyle-Lunders, Lyndsay; Harsin-Waite, Amanda; Hofman, Nicole; Knutson, Lacy M.
Publication:The Behavior Analyst Today
Article Type:Report
Date:Jan 1, 2012
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