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TEMPORAL DYNAMICS OF PERCEPTUAL DECISION
by
Wilson Chu
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PYSCHOLOGY)
May 2008
Copyright 2008 Wilson Chu
Object Description
| Title | Temporal dynamics of perceptual decision |
| Author | Chu, Wilson |
| Author email | wilsonchu333@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Psychology |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2007-03-08 |
| Date submitted | 2008 |
| Restricted until | Restricted until 11 Apr. 2010. |
| Date published | 2010-04-11 |
| Advisor (committee chair) | Lu, Zhong-Lin |
| Advisor (committee member) |
Tjan, Bosco Manis, Franklin Hellige, Joseph Hirsch, Judith |
| Abstract | We combined the external noise method (1) with the cue-to-respond speed accuracy trade-off (SAT) paradigm (2) to characterize the temporal dynamics of perceptual decision making. Observers were required to identify the orientation of one of eight briefly presented peripheral Gabor targets (+/- 12 deg) in both zero and high noise. An arrow, occurring in the center of the display cued the observer to the target location 234 ms before the onset of a brief target display; an auditory beep, occurring at one of eight delays (SOA=25 to 800 ms) after the target onset, cued the observers to respond. Five Gabor contrasts, spanning a wide range of performance levels, were tested in each external noise condition. Increasing accuracy of discrimination (d ) was measured over processing times from 210 to 940 ms (as a function of SOA to the cue) in each external noise and Gabor contrast condition. All ten SAT functions were well fit by exponential functions with identical time constant and intercept but different asymptotic levels. This suggests that, despite enormous variation in the external noise and contrast energy in the stimulus, and in the ultimate accuracy of performance, information accumulated with the same rate and starting time across all the external noise and contrast conditions. In addition, we conducted a standard response time version of the experiment both before and halfway through the SAT procedure. Data from the response time version of the experiment were all consistent with the speed-accuracy trade-off data, but primarily differed in response accuracy. A simple elaboration of the perceptual template model (3) with a dynamic decision process in which information accumulates with the same rate but with step sizes proportional to the signal to noise ratio in the perceptual representation of the visual input fully accounts for the results.; The cued-to respond Speed-Accuracy Tradeoff (SAT) paradigm (1) combined with external noise manipulations was used to evaluate the effects of perceptual learning on the temporal dynamics of perceptual decision. Observers were trained in a 2AFC Gabor (+/- 12°) orientation-discrimination task in eight sessions. An auditory beep occurred at one of 8 delays (SOA = 25ms to 800ms) that cued the subjects to respond. Subject's performance was constrained to 79.1% and 70.7% correct at the longest SOA by a 3-to-1 and a 2-to-1 staircase respectively that adjusted the contrast of the signal stimuli. All subjects showed learning, demonstrated by an average reduction of contrast threshold levels of 23% in high noise and 22% in low noise. An elaborated perceptual template model with a dynamic decision process (2) provided very good fits to the data. The best-fitting model included identical time constant and intercept (t0) across all the training sessions. The result suggests that perceptual learning enhances stimulus (in the zero external noise condition) and excludes external noise (in the high external noise condition) without altering the temporal dynamics of perceptual decision. |
| Keyword | perceptual decision; perceptual learning; psychophysics |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Type | texts |
| Legacy record ID | usctheses-m1094 |
| Contributing entity | University of Southern California |
| Rights | Chu, Wilson |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Chu-20080411 |
| Archival file | uscthesesreloadpub_Volume26/etd-Chu-20080411.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Full text | TEMPORAL DYNAMICS OF PERCEPTUAL DECISION by Wilson Chu A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (PYSCHOLOGY) May 2008 Copyright 2008 Wilson Chu |
