Biomedical subjects

J D Crystal

Publications and source records attributed to J D Crystal.

4 recordsLinked to original sources

PubMed2001

Circadian time perception.

The variability of anticipating a meal was investigated. Sprague-Dawley rats earned food by inspecting a food source during a 3-hr interval. Food was not available at other times. In Experiment 1, the meal started 3 or 7 hr after light offset in a 12-hr light-dark cycle. Experiment 2 was conducted in constant darkness with 14-, 22-, 22.5-, 24-, 25.5-, 26-, or 34-hr intermeal intervals. Inspections increased before the meal. Rats timed intervals in the circadian range (22-26 hr) with lower variability than that for intervals outside this range (3-14 and 34 hr). Higher precision in timing selected intervals violates the scalar property. Proximity to a circadian oscillator improves timing precision. Variability may be used to identify oscillators with noncircadian periods.

Animals↗

PubMed1999

Systematic nonlinearities in the perception of temporal intervals.

Rats judged time intervals in a choice procedure in which accuracy was maintained at approximately 75% correct. Sensitivity to time (d') was approximately constant for short durations 2.0-32.0 s with 1.0- or 2.0-s spacing between intervals (n = 5 in each group, Experiment 1), 2.0-50.0 s with 2.0-s spacing (n = 2, Experiment 1), and 0.1-2.0 s with 0.1- or 0.2-s spacing (n = 6 in each group, Experiment 2). However, systematic departures from average sensitivity were observed, with local maxima in sensitivity at approximately 0.3, 1.2, 10.0, 24.0, and 36.0 s. Such systematic departures from an approximately constant d' are predicted by a connectionist theory of time with multiple oscillators and may require a modification of the linear timing hypothesis of scalar timing theory.

Animals↗

PubMed1998

Temporal search as a function of the variability of interfood intervals.

We attempted to determine whether timing theories developed primarily to explain performance in fixed-interval reinforcement schedules are also applicable to variable intervals. Groups of rats were trained in lever boxes on peak procedures with a 30-, 45-, or 60-s interval, or a 30- to 60-s uniform distribution (Experiment 1); a 60-s fixed and 1- to 121-s uniform distribution between and within animals (Experiment 2); and a procedure in which the interval between food and next available food gradually changed from a fixed 60 s to a uniform distribution between 0 and 120 s (Experiment 3). In uniform interval schedules rats made lever responses at particular times since food, as measured by the distribution of food-food intervals, the distribution of postreinforcement pauses, and the mean response rate as a function of time since food. Qualitative features of this performance are described by a multiple-oscillator connectionist theory of timing.

Animals↗

PubMed1997

Systematic nonlinearities in the memory representation of time.

The representation of time was investigated by testing rats with intervals that changed by 2 s across trials. In Experiment 1, 2 ranges (20-150 s, 30-160 s; n = 10 rats per group) were examined. The times at which response bursts occurred (start time) were approximately proportional to interval durations. However, systematic departures from linearity were observed. Nonlinearities were related to the absolute duration of intervals, rather than to durations relative to the range. In Experiment 2, 660-s trials were inserted into the sequence of intervals (10-140 s, n = 20). Start and end times of response bursts were approximately proportional to intervals, but nonlinearities in start and end times were correlated, indicating that the source of nonlinearity was in the memory representation of time rather than in a decision process. These results indicate that the representation of time is nonlinearly related to physical time.

Animals↗