Effect of varying the duration of grain presentation on automaintenance

In a series of three experiments the effects of variation in grain duration on automaintenance were evaluated. In the first experiment, key illumination was followed by grain only when pigeons did not peck the key. Each subject was exposed to 2-, 4-, and 8-second feeder durations in blocks of 10 sessions. Subjects pecked on a high percentage of trials at all feeder durations. The mean peck latency was shorter in the 8-second condition than in the two other conditions in five of six subjects. The conditional probability of pecking given successive keylight-grain pairings did not increase as the number of pairings increased. The second experiment was identical to the first, except that key pecking had no scheduled consequence. Under these conditions, all three subjects showed substantial responding. The recorded measures showed no systematic relationship to feeder duration in this study. In the third experiment, two different stimuli were followed by feeder presentations of either identical (2- or 8-second) or different (2- and 8-second) durations within each session. Subjects tended to respond sooner and with a higher overall rate in the presence of the stimulus associated with the longer feeder duration only when different feeder durations were presented within the same session. This result was confirmed by direct observation of the pigeons. The results of these experiments suggest that the effects of varying grain duration may be small, compared to the effects of varying other variables. The results also suggest that the location as well as the frequency of pecking may be an important measure in the analysis of factors controlling the pigeon's key peck.     

Effect of stimulus duration on perceptual onset and offset latencies

The effects of stimulus duration on perceptual onset and offset latency were compared in vision and audition. It was found that perceptual onset latency was independent of stimulus duration but that the perceptual offset latency was longer for brief stimuli than for stimuli that exceeded a critical duration. For stimuli longer than the critical duration, the perceptual onset and offset latencies were equal: The same temporal relationships were found in both modalities. The results indicate that for any specific stimulus parameters, reduction of stimulus duration results, ultimately, in a perception of fixed duration.     

Effect of stimulus duration on stereo and vernier displacement thresholds

Stereo and vernier thresholds were determined as a function of stimulus duration in both misalignment and displacement paradigms. All four thresholds increase as stimulus duration decreases. The increase is greatest for the stereo displacement threshold, less for the vernier displacement threshold, and least for the misalignment thresholds. The results are consistent with the hypothesis that depth signals are averaged over time.     

On the discriminability of stimulus duration.

The performance of pigeons trained to detect differences in the duration of stimuli was analysed using a matching model of signal detection. Two white stimuli, S1 and S2, differing in duration, were arranged with equal probability on the center key of a three-key chamber. S1 was systematically varied from 5 seconds to 25 seconds while S2 remained constant at 30 seconds. On completion of the center-key stimulus, a peck on the center key turned on the two red side keys. A left-key response was "correct" when S1 had been in effect on the center key and a right-key response was "correct" on S2 trials. A correct response produced a 3-second magazine light accompanied intermittently by food. Incorrect responses produced 3-second blackouts. Detection performance was measured under two procedures. In the first, the obtained reinforcement ratio was uncontrolled by allowing the number of food reinforcements obtained for correct left- and right-key responses to vary as the stimuli were changed. In the second procedure, the presentation of food reinforcement was controlled by holding the obtained reinforcement ratio constant. Discriminability changed as a function of stimulus differences under both procedures. No such trend was found in response bias.     

The effect of stimulus duration on the persistence of gratings

The persistence of gratings varying in spatial frequency and exposure duration was measured using a stimulus-blank alternation method. Persistence was found to lengthen with increasing spatial frequency and to shorten with increasing exposure duration. For each spatial frequency, persistence decreased linearly with a slope of approximately —.75 as duration increased for short stimulus durations. For longer stimulus durations, the rate of decline in persistence with increasing duration was reduced, the slope being approximately —.13. The stimulus duration at which the change in slope of the persistence-duration relationship occurred was shown to increase with increasing spatial frequency and was approximately equivalent to the critical duration for each spatial frequency. The data were consistent with an interpretation of persistence in terms of a temporal integration component and a second, possibly cortically located, component.     

Intervening stimulus effects on category judgments of duration

Auditory pulses (1,000 Hz) occurring between the 500-Hz bounding markers of durations being judged were varied in their position and number over three experiments which examined the effects of these factors on measures of amount of filled-duration illusion (FDI) and interduration discriminability. The results establish that the locus of the FDI is postattentive, since some of the incoming sensory information, selected on the basis of simple physical cues, can be excluded from further processing. FDI decreases both when the intervening stimuli come from a different source (earphone channel) to the marker stimuli and when they appear as part of an ongoing sequence of background pulses. Discrimination of durations containing intervening stimuli is enhanced if the filler events are placed such that repetitions of a given subinterval result. Thomas and Brown’s (1974) “chunking” model can account for the observed effects with the additional assumption that the error associated with encoding a given subinterval is sequentially modified as a function of number of recent encodings.     

Control of responding by stimulus duration

Pigeons were trained on a procedure in which the key was white for 30 sec, alternating with periods of darkness, or timeout. In a nondifferential training procedure, timeout duration was held constant at either 9 or 21 sec for different animals, and pecks on the white key were reinforced on a variable-interval 36-sec schedule. After 30 sessions an extinction generalization test was conducted where the duration of the timeout was varied from 3 to 27 sec. This test showed no differences in responding following timeouts of different durations. In a differential training procedure, timeout durations of either 9 or 21 sec were randomly scheduled for each animal. The variable-internal schedule was in effect following the same timeout duration as in the prior nondifferential procedure. No pecks were reinforced after the other timeout duration. In 40 sessions, differences in response rates following the two durations gradually developed. A maintained generalization procedure was then imposed in which timeout durations were varied from 3 to 27 sec, with the variable-interval schedule in effect following only the same duration as in the previous procedures. The first maintained generalization session showed that the prior differential training had established control of the animals' behavior by the timeout duration. In continued training on the maintained generalization procedure, control by the timeout duration decreased.     

Response bias and the discrimination of stimulus duration

Pigeons discriminated stimulus duration in a psychophysical choice situation. Following presentation of any duration from a set of short duration (11 to 15 sec), responses on a red key were reinforced intermittently. Following presentation of any duration from a set of long durations (16 to 22 sec), responses on a green key were reinforced intermittently. Relative reinforcement rates were manipulated for choice responses across conditions. As relative reinforcement rates were varied, psychometric functions showed shifts in green-key responses at all durations. A signal-detection analysis showed that sensitivity remained roughly constant across conditions while response bias changed as a function of changes in relative reinforcement rate. Relative error rates tended to match relative reinforcement rates.     

Relative judgments affect assessments of stimulus duration

Humans were trained on two independent temporal discriminations, with correct choice dependent on the initial stimulus duration. In Experiment 1, the durations were 1.0 and 4.0 sec, with one set of choice stimuli, and 2.0 and 8.0 sec, with a different set of choice stimuli. The 2.0- and 4.0-sec values were selected to be the geometric mean of the two values in the other discrimination. In Experiment 2, the durations were 2.0 and 5.0 sec for one discrimination and 3.5 and 6.5 sec for the other. The 3.5- and 5.0-sec values were selected to be the arithmetic mean of the two values in the other discrimination. In both experiments, participants showed evidence for relational coding of the duration pairs. That is, the test durations were selected to be at the presumed bisection point (i.e., they should have produced indifferent choice), but instead the shorter test duration from the longer duration pair produced a “short” bias (in both experiments), whereas the longer duration from the shorter duration pair produced a “long” bias (in the second experiment). Results were similar to those from Zentall, Weaver, and Clement (2004) with pigeons.     

Conditioning across the duration of a backward conditioned stimulus

Five conditioned suppression experiments examined the extent to which an appetitively motivated lever-press response can be punished by different components of a backward conditioned stimulus (CS). Using a 0-s unconditioned stimulus (US)-CS interval, Experiments 1 and 2 showed that the initial 3 s of a normally 30-s backward CS served as a more effective punisher than the CS as a whole. Experiment 3 found no such effect if the US-CS interval were 3 s rather than 0 s. Experiments 4A and 4B found that if the US-CS interval were 0 s, the initial part of the backward CS acquired excitatory properties although the CS as a whole passed a summation test for conditioned inhibition. By contrast, the 3-s US-CS interval supported inhibitory conditioning across the whole duration of the backward CS. Taken together, these findings support a modified version of Wagner's sometimes opponent process model, which suggests that different components of a backward CS become either excitatory or inhibitory depending on the components' temporal proximity to the US.