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Auditory Perception Laboratory (APL)

Dr. Ian A. Harrington

If you are an Augustana student interested in auditory sensory and perceptual research, contact me at 794-7243 or send me an e-mail.

Lab Overview:

We are interested in understanding auditory perception in human listeners. The lab is located in room 325 on the 3rd floor of Sorensen Hall, and is currently equipped with two personal computers running MATLAB, Audacity, SPSS for Windows, and other software. The lab also has multi-channel soundcards, headphone and power amplifiers, a variety of headphones and loudspeakers for stimulus presentation, measurement equipment, and an excellent autonomous, diffuse-noise generator (the lab's overzealous ventilation system).

Ongoing Projects:

  • Within- and between-channel gap detection:

    The first study conducted by the lab addressed the following question: How well can listeners detect brief silent periods between sounds? Pretty well, it turns out, provided the sounds that precede and follow the gap are presented to the same ear. Under these conditions, gaps as short as 2 milliseconds are reliably detected by most listeners. But what happens when these sounds are presented to different ears and your brain has to stitch the end of the first sound to the beginning of the second? In this case, listeners are far less sensitive and require gaps to be up to10-20 times longer. This project was completed during the 2005-06 academic year and was presented at the on-campus Celebration of Learning.

  • Effect of bandwidth on between-channel gap detection:

    In our first study, the lab was able to replicate all of the main within- and between-channel gap detection phenomena demonstrated by others, except one. In previous studies, most notably that of Phillips and colleagues (1997), in addition to an overall elevation of gap thresholds in the between-channel case, thresholds were also sensitive to the duration of the sound that precedes the gap (i.e., the leading marker). Specifically, thresholds were highest for the shortest leading markers (5-30 ms) and decreased as the duration of the leading marker was increased up to 300 ms. In our experience, although between-channel thresholds were higher for the shortest leading markers (5 and 10 ms) and decreased at slightly longer durations (30 and 50 ms), thresholds increased again for even longer leading marker durations (100 and 300 ms) and were more comparable to those seen at short leading marker durations.

    Why the discrepancy between our results and those of Phillips and colleagues (1997) at longer leading marker durations? One explanation involves the fact that their sounds had a smaller bandwidth than those used in our study. The bandwidth of a sound refers to the range of sound frequencies it contains: the higher the bandwidth, the broader the range. We addressed this possibility by determining between-channel gap thresholds for sounds of different bandwidths. The results of this study demonstrated that between-channel gap thresholds were independent of stimulus bandwidth over the range from 1/4 to 4 octaves. Thresholds were again lower for leading markers with intermediate durations (50 ms) than either shorter (5 ms) or longer (300 ms) durations.

  • Are there sex differences in between-channel gap detection?

    At the conclusion of the last study, we observed that the magnitude of these between-channel effects could vary dramatically from one participant to the next but that the effects tended to be larger in females than males. By combining comparable data from the first two studies we were able to analyze the effect of participant sex on gap thresholds with leading markers having durations of 5, 50 and 300 ms. The results of these preliminary analyses indicate that while males and females perform equivalently at 50 ms, the thresholds of females are considerably elevated at shorter or longer durations. Indeed, among several of the male participants, the effects of leading marker duration on gap thresholds were negligible. These findings suggest that much of the effect we see overall is driven by the behavior of our female participants.

    As a follow-up to our initial studies of well-trained listeners, we have completed a study of between-channel gap detection in 31 novice listeners (7 male). The results suggest that the leading-marker-duration effect is robust enough to be demonstrated in short-term testing of naive participants. Moreover, the thresholds of our female listeners were elevated by approximately 10 ms over those of our male listeners. In contrast to our experienced listeners, however, the thresholds of our naive listeners were elevated at all leading marker durations.

Current Personnel:

  • Peter Bowling
  • Jim Clinton
  • Anne-Jessica Steed
  • Kyle Lenz

Alumni:

  • Kurt Albrecht
  • Meaghan Bychowski (University of Wisconsin program in Neuroscience)
  • Christine Day
  •  Kristen Kaseeska
  • Rob Murphy
  • Carl Jannusch
  • Selvan Thamilavel
  • Yancy Gillespie

Presentations:

  • Bychowski, M. E., Day, C. G., Thamilavel, S., & Gillespie, Y. L. (2006). Mind the gap: Within- and between-channel gap detection by human listeners. Presented at the Celebration of Learning, Augustana College.
  • Clinton, J. A., Murphy, R. C., Bowling, P. J., Albrecht, K. M., Thamilavel, S., Kaseeska, K. R., & Steed, A- .J. (2007). In one ear, then in the other: Effects of stimulus bandwidth on between-channel gap-detection abilities. Presented at the Celebration of Learning, Augustana College.
  • Steed, A-. J., Kaseeska, K. R., Thamilavel, S., Albrecht, K. M., Bowling, P. J., Murphy, R. C., & Clinton, J. A. (2007). What's sex got to do with it? Sex differences in between-channel gap-detection abilities. Presented at the Celebration of Learning, Augustana College.
  • Clinton, J. A., Bowling, P. J., & Steed, A-. J. (2007). Between-channel gap detection in naive listeners: Sex differences. Presented at Tri-State Undergraduate Psychology Conference, Rockford College, Rockford, IL.
  • Harrington, I. A., Clinton, J. A., Bowling, P. J., & Steed, A-. J. (2007). Between-channel gap detection: effects of stimulus duration, bandwidth, and participant sex. To be presented at the meeting of the Midwestern Psychological Association, Chicago, IL.