Dopamine agonists and antagonists can produce an attenuation of response bias in a temporal discrimination task depending on discriminability of target duration

Disruptive effects of stimulus intensity on two variations of a temporal discrimination procedure

Previous reports using stimulus intensity changes to disrupt temporal discrimination have shown shifts in the psychophysical curve for time, while studies using other disruptors have shown a flattening of the curve. The current study investigated the impact of increases and decreases in stimulus intensity on temporal discrimination in pigeons, to determine if a flattening of the curve could be extended to this disruptor. The brightness of the sample to be timed was manipulated under two procedural variations, in which the response alternatives were differentiated by color or location. Results showed that all subjects in the color procedure, and one in the location procedure, showed a flattening of the psychophysical curve when they experienced increased stimulus intensity in descending order. No subjects exposed to an ascending order of stimulus intensities, and none of the other subjects in the location procedure, showed any impact of changed stimulus intensity. Minimal disruption was found when test sessions presented decreased stimulus intensity levels in a second series. These results, together with those using other types of disruptors, add to the evidence of a flattening of the psychophysical curve when temporal discrimination is disrupted.

ABA chronic dosing of D-amphetamine produces differential drug effects in two variants of a temporal discrimination procedure in pigeons

The impact of two procedural variants of the matching to sample of duration procedure on the effects of chronically administered D-amphetamine on temporal discrimination was assessed. The task consisted of subjects classifying durations as short or long to produce a psychophysical curve for time. Procedural variations included response alternatives being defined by either the location of the response keys (Location), or by their color (Color). During Phase 1, two groups of pigeons experienced one of these procedures while being administered with D-amphetamine in an ABA chronic dosing regimen. Phase 2 was a reversal condition in which select birds from Phase 1 were trained on the other procedural variation that they had not experienced and were again given D-amphetamine in an ABA chronic regimen. Results showed that during Phase 1, subjects in the Color group showed a flattening of the psychophysical curves during amphetamine administration, whereas those in the Location group showed a shift of the psychophysical curve to the left and right. Phase 2 revealed that subjects who had experienced the Location variant first were less disrupted by the drug, even when experiencing the Color condition. The procedural variation, dosing regimen, and form of data analysis all provide more information regarding the cause of discrepancies in the timing literature regarding differential effects of D-amphetamine on timing behavior.

Effects of acute and chronic d-amphetamine on two variations of a temporal discrimination procedure

This study assessed temporal discrimination using a procedure in which pigeons classified temporal intervals as short or long based on different responses following visually presented stimulus durations. For the Location group, response alternatives were defined by the location of response keys, whereas for the Color group response alternatives were defined by key color. Temporal parameters were derived from psychophysical curves for time, and the impact of d-amphetamine was determined during acute and chronic dosing. Results showed that classification of temporal intervals was disrupted dose dependently during the acute drug assessment, regardless of the procedural variation. During the chronic drug assessment, differences in one of the psychophysical parameters, Range, were found between groups, as well as a significant effect of Dose on Standard Deviation values in the Color group. These data suggest that procedural variation does not lead to differential effects of d-amphetamine when administered in an acute regimen; however, differences found during chronic administration suggest that procedural variations may influence the development of tolerance as evidenced by differing Range values between groups and marked disruption of Standard Deviation values at the low dose in the Color group. The influence exerted on temporal behavior and tolerance by procedural variations during acute and chronic regimens of d-amphetamine should be explored further.

The effect of Parkinson’s disease on time estimation as a function of stimulus duration range and modality

The present research sought to investigate the role of the basal ganglia in timing of sub- and supra-second intervals via an examination of the ability of people with Parkinson's disease (PD) to make temporal judgments in two ranges, 100-500 ms, and 1-5 s. Eighteen non-demented medicated patients with PD were compared with 14 matched controls on a duration-bisection task in which participants were required to discriminate auditory and visual signal durations within each time range. Results showed that patients with PD exhibited more variable duration judgments across both signal modality and duration range than controls, although closer analyses confirmed a timing deficit in the longer duration range only. The findings presented here suggest the bisection procedure may be a useful tool in identifying timing impairments in PD and, more generally, reaffirm the hypothesised role of the basal ganglia in temporal perception at the level of the attentionally mediated internal clock as well as memory retrieval and/or decision-making processes.