Seven subjects participated in a dichotic listening task and judged in which ear the leading stimulus was presented. The stimuli consisted of six speaker-produced stop consonant-vowels, /ba/, /da/, /ga/, /pa/, /ta/, and /ka/ which were digitally edited to durations of 40, 60, 90, and 180 msec. The experiment was blocked by stimulus duration. At each condition of duration, listeners judged the temporal order of stimuli separated by 4, 8, 16, 32, or 64 msec asynchrony. There were significant main effects of both asynchrony and stimulus duration. Sensitivity increased with longer asynchronies and also for longer durations. Thresholds, between 16 and 32 msec asynchrony, approximated those reported by others. A further comparison of intensity levels, 66 dB SPL and 100 dB SPL, for the 40 msec duration condition proved non-significant. The results are compared to earlier investigations which reported increases in sensitivity for shorter duration stimuli, but which, in all cases, employed monotonically presented sinusoids. The results of the present study suggest that stimulus duration affects temporal order judgment at central as well as peripheral levels of processing / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

The effects of deprivation and repeated shifts on positive and negative contrast effects in the albino rat were investigated. Six groups, formed by a factorial combination of two deprivation levels (deprived or non-deprived) and three concentration conditions (4%, 32%, or alternating 32% and 4% every two days), were used. Fifty-seven subjects were given daily five-minute exposures to a 32% or 4% sucrose solution. Experimental alternation groups received a total of five upshifts to the 32% solution and five downshifts to the 4% solution. Control groups received only the 32% or 4% solution, respectively, throughout the 22 day test period. Negative contrast was repeatedly obtained, with both deprived and non-deprived alternating subjects lower than the 4% control subjects on dependent measures of lick rate and time spent at the drinking tube. Recovery was noted in deprived subjects on the second day of each downshift; non-deprived subjects displayed a negative contrast effect which endured across both days. Positive contrast was apparent, with deprived alternating subjects scoring above 32% control subjects in the first shift only. Non-deprived subjects did not exhibit positive contrast, but rather displayed means below that of the non-deprived control groups. The negative contrast results indicated that deprivation level yielded differences in contrast effects, due possibly to subjects in different deprivation conditions responding to different aspects of the same solution. Positive contrast results indicated that a 'ceiling effect' may limit the possibility of demonstrating positive contrast for deprived subjects. The results were discussed in terms of a perceptual/emotional model, which suggests that the mechanisms responsible for contrast change over time / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu