Rapidly induced auditory plasticity: The ventriloquism aftereffect
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Figure 1Psychophysical paradigms used to demonstrate the ventriloquism aftereffect. (A) The experimental strategy. Subjects first had their absolute localization ability measured, then were exposed for a period of 20–30 min to paired visual and auditory stimuli, then had their absolute localization ability remeasured. (B) The absolute localization paradigm used pre- and posttraining for each subject. (C) Training paradigm for the ventriloquism aftereffect. The 15-speaker array with a corresponding LED for each speaker is schematically illustrated. The subject pressed a button to initiate a trial. Throughout the course of the session a light and sound were simultaneously presented in a consistent spatial relationship. In this example the light is located two positions (8°) to the right of the sound. The subject was asked to attend to the intensity of the acoustic stimuli and to release the button on detection of a decrease in intensity.
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Figure 2Single trial estimates from subject 1 localizing a 750 Hz tone before (long vertical lines) and after (short vertical lines) 2,500 trials of the training paradigm as described in Fig. 1 C. This figure shows five of the nine tested locations, offset vertically for clarity. Target location is indicated by the thick, shaded bar.
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Figure 3Summary of the aftereffect experiments across subjects (symbol type) for the 750 Hz stimulus (open symbols) and 3,000 Hz stimulus (solid symbols; see Inset). (A) Results from the +8° disparity during the training period. The mean estimates for each speaker location were taken pre- and posttraining and subjected to regression analysis. These data were significantly correlated, and the resulting regression line had a y-axis offset of +7.08°. The regression equation, r, and P values are given in the Inset. Dashed line, perfect correlation; heavy line, regression line. (B) Results from the 0° disparity during the training period. Conventions are as A. The dashed line of perfect correlation is occluded by the regression line.
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Figure 4Demonstration of the ventriloquism aftereffect by using a nonspatial response paradigm. (A) The psychophysical task differed from the absolute localization paradigm in that the subjects kept their head stationary throughout the session and initiated each trial with a lever press. A single LED was illuminated for 200 msec, followed by a 300-msec pause, and then a 200-msec tone was presented. The subjects responded to a perceived difference in the spatial location between the tone and the light by releasing the lever within 500 msec, or a new trial was initiated. No feedback was given. A single session consisted of three different LED locations (−12, 0, and +12°) and nine speaker locations spanning a region ±16° of each LED. A complete session consisted of 120 trials for each matching LED and speaker location, and 15 trials at each nonmatching LED and speaker location (720 trials total). (B) Representative psychometric functions from Subject 3. The percent of trials in which the subject released the lever is plotted as a function of the distance between the light and tone stimulus locations. The heavy line shows the percent of responses before training, whereas the thin line shows the data from the same subject immediately after training. Only trials in which the LED was located at position 0 are shown for clarity.
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Figure 5Representative tuning function from two single neurons recorded in physiologically defined primary auditory cortex in a macaque monkey trained to perform a sound localization task. A total of 496 different stimuli (50 msec; 5 msec rise/fall) were presented, spanning a range of 31 frequencies (25–5,000 Hz in equal octave steps) and 16 intensities (5–75 dB SPL). Each stimulus was presented twice, and the average response of the neuron is shown as the shaded region. Regions of the plots that are not shaded represent responses that were not greater than two times the spontaneous activity. Activity was recorded for 100 msec from stimulus onset. Data for both panels are taken from single neurons recorded in the left hemisphere of one monkey in regions physiologically corresponding to cortical area AI (41–43) of auditory cortex. Arrows indicate the responses at 45 dB SPL.
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Figure 6No transference of the aftereffect across frequencies. This plot shows the data collected across subjects and frequencies similar to that shown in Fig. 3 A. The training period was always the frequency not used in the testing paradigms. The regression analysis indicates that there is no difference between the pre- and posttraining periods.
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Figure 7Cumulative percent of neurons with the latencies of different portions of the response. The dashed line shows the cumulative percent of neurons with the latency of the first response represented on the x axis. The thin line shows the latency of the peak response. The thick line represents the cumulative percent of neurons that have decreased their activity to below 25% of the peak response by the latency indicated on the x axis. Stimuli consisted of 200-msec tone bursts (50 ± 10 dB SPL) at the characteristic frequency of the neuron. Data were taken as the averaged response over 10–12 trials for stimuli presented at 0° azimuth. The monkey was performing a go/no-go sound localization task in which 7–12 stimuli were presented at +90°, and the monkey had to make a lever response when it detected a change in location to one of nine speakers located within ±30°. Data were analyzed only for hit trials.
Footnotes
- Copyright © 1998, The National Academy of Sciences
