Abstract
The present study investigated temporal perception in a Huntington disease transgenic rat model using a temporal bisection procedure. After initial discrimination training in which animals learned to press one lever after a 2-s tone duration, and the other lever after a 8-s tone duration for food reward, the bisection procedure was implemented in which intermediate durations with no available reinforcement were interspersed with trials with the anchor durations. Bisection tests were repeated in a longitudinal design from 4 to 8 months of age. The results showed that response latencies evolved from a monotonic step-function to an inverted U-shaped function with repeated testing, a precursor of non-responding on trials with intermediate durations. We inferred that temporal sensitivity and incentive motivation combined to control the transformation of the bisection task from a two-choice task at the outset of testing to a three-choice task with repeated testing. Changes in the structure of the task and/or continued training were accompanied by improvement in temporal sensitivity. In sum, the present data highlight the possible joint roles of temporal and non-temporal factors in the temporal bisection task, and suggested that non-temporal factors may compensate for deficits in temporal processing.
Highlights
The temporal bisection procedure has been used extensively to study temporal perception in animals
The latter trend was evidenced in a sharp decrease in the mean percent of trials with a response as intermediate values approached the 4-s geometric mean of the anchor duration values, and an increase in mean response latency which peaked near the geometric mean of the anchor durations (Figures 1A,B)
Repetition resulted in a sharpening of the bisection function and discrimination between anchor durations and intermediate test durations, both of which were more pronounced in tgHD rats
Summary
The temporal bisection procedure has been used extensively to study temporal perception in animals. The procedure is a variant of the classical psychophysical method of constant stimuli. It entails an initial conditional discrimination training phase in which one response is rewarded following a short-duration stimulus, while the other response is rewarded following a long-duration stimulus. A virtue of the method is that it can provide separate measures of the point of subjective equality (PSE), difference limen and Weber fraction that are extracted from the resulting psychometric function. Variations in these measures are assumed to reflect the operations of fundamental mechanisms of temporal perception
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