Retention interval and intertrial interval in a serial learning or delayed discrimination task

In each of four experiments, rats were provided with the same three-event decreasing series (18-1-0) of 0.045-g food pellets in a runway. Tracking, running fast to 18 pellets and running slow to 1 and 0 pellets, was investigated as a function of the temporal interval elapsing between the events of the series (the retention interval), shifts in retention interval, and number of trials each day (or the intertrial interval), a trial being defined as presentation of each of the three events of the series. Neither retention interval, which varied from 15 s to 30 min in various investigations, nor shifts in retention interval affected tracking when only one trial was given each day. But when more than one daily trial was given, tracking was acquired more slowly and was disrupted by a shift in retention interval from 15 s to 5 min. Tracking was also disrupted by a shift from one to two trials each day. These results indicate that when given one 18-1-0 trial each day, the rat partitions events on a first-event/subsequent-event basis; that little forgetting occurs even at long retention intervals; that somewhat different memories signal events when one or more than one 18-1-0 trial occurs each day; and that retention interval deficits can arise owing to the same or similar memories' signaling different events. The results described limit the generality of three hypotheses suggested in two recent investigations: that as retention interval increases, rats find it increasingly difficult to remember and utilize serial position cues; that tracking in serial tasks is not influenced by number of trials each day; and that there are specific stimuli associated with each retention interval which, when changed, necessarily disrupt performance.     

Multiple repetition priming of faces: Massed and spaced presentations

Previously viewing a face typically leads to a decrease in the amount of time taken to later identify it (“repetition priming”). Five repetition priming experiments are reported, which investigate whether multiple presentations of a face increase the amount of repetition priming. The results demonstrate similar amounts of priming from massed multiple presentations of the same face or a series of different images (freeze frames selected from a moving clip and presented in sequence), compared with a single unchanging presentation (Experiments 1 and 2). This is true even when different images are presented at prime and test (Experiment 3). However when multiple presentations were presented in a spaced fashion, with one or more intervening items between each repeat, there was significantly more priming in the multiple than single presentation condition (Experiment 4). This was true even when the face was named only once in both the multiple and single spaced conditions (Experiment 5). The results are discussed in relation to face motion.     

The role of context in intertrial interval effects in autoshaping

Two experiments evaluated the role of differential conditioning of the context in mediating the effect of intertrial interval (ITI) in autoshaping. In Experiment 1 pigeons were given acquisition with two keylights, each presented in a particular context. A given keylight/context combination had associated with it either a short (10-sec) or a long (2-min) ITI. Acquisition was more rapid with the long ITI. Tests with those keylights in a common third context indicated that the longer ITI had resulted in greater conditioning. On the other hand, pigeons trained on keylights with mixed ITIs in a third context evoked more responding when they were tested in the short ITI context compared with the long ITI context. That suggests that a context with a history of a short ITI enhances performance. In Experiment 2, two keylights were initially conditioned with mixed ITIs and then extinguished in different contexts under different ITI lengths. Extinction was more rapid for the keylight presented with a short ITI. That difference persisted when the keylights were tested with mixed ITIs in a common third context, suggesting a difference in associative strength of the keylights. The results are interpreted in terms of differential context conditioning resulting in differences in learning about the keylight.     

Massed vs. spaced exposure sessions in the treatment of agoraphobia

The differential effects of massed and spaced sessions of exposure in vivo were investigated with 11 agoraphobics in a crossover design. Clients were randomly assigned to one of the following two groups: (a) 10 daily sessions followed by 10 weekly sessions, or (b) 10 once-weekly sessions followed by 10 daily sessions. The results indicated that both massed and spaced sessions of exposure in vivo effected changes in avoidance behavior and subjective anxiety of agoraphobics, massed practice being superior especially with respect to avoidance. It was suggested that the superiority of massed practice is due to the lack of opportunity to engage in avoidance or escape during short inter-session intervals. The relationship between subjective anxiety and avoidance were considered and the differences between clinical and statistical significance were discussed.     

The role of nonreinforcement in the learning of honeybees

Two series of experiments with honeybees were designed to test the assumption that inhibition is generated by nonreinforcement as a function of the excitatory value of the context. In the first series (Experiments 1-3), summation tests with B were made after A+/C-/AB- as compared to A+/C-/CB- training, with precautions taken to minimize the possibility of a masking effect of excitatory within-compound conditioning on AB trials; responding to B did not vary with training procedure. In the second series (Experiments 4-5), retardation tests rather than summation tests were used, in the belief that they might be more sensitive; after A+/AB-/CD- training, acquisition in a B+/D- problem was found to be no less rapid than in a D+/B- problem. A third series of experiments (Experiments 6-9) was designed to test the more general assumption that the effectiveness of nonreinforcement increases with the excitatory value of the context; response to B was found to be no different after A+/B+/C- training followed by A+/AB- training than after A+/B+/C- training followed by A+/CB- training. The results are compatible with the view that the role of nonreinforcement in honeybees is not to generate inhibition, but only to reduce excitation in a manner independent of the excitatory value of the context.     

Function of intertrial interval in matching-to-sample

Twelve pigeons were trained on matching-to-sample using either a 0-, 5-, 15-, 25-, or 60-sec intertrial interval. Eight of these 12 pigeons were given one of the following intertrial interval changes: 0 to 60, 0 to 5, 5 to 0, 60 to 0, 15 to 25, 5 to 15, 60 to 5, 5 to 1, 1 to 5, 1 to 25, and 25 to 1 sec. Most intertrial interval changes were repeated at least once. The 0-sec intertrial interval subjects failed to match beyond chance levels, while other intertrial interval values resulted in matching acquisition. Changes from 0 sec to other intertrial interval values increased and changes to 0 sec decreased matching performance. Changes to intertrial interval values other than 0 sec resulted in little change in matching accuracy once stable performance had been attained.     

Temporal factors influencing the pigeon's successive matching-to-sample performance: sample duration, intertrial interval, and retention interval

A successive matching-to-sample procedure that entails the sequential presentation of sample and test stimuli and the monitoring of response rates in a go/no-go discrimination of matching and nonmatching stimuli was studied as an alternative to the familiar delayed-matching paradigm of animal short-term memory. Three within-subject experiments studied the effects of sample duration (1 to 12 seconds), intertrial interval (5 to 50 seconds), and retention interval (1 to 50 seconds) on the pigeon's successive-matching performance. The results revealed that retention was (a) an increasing function of sample duration and intertrial interval, and (b) a decreasing function of retention interval. These results were in accord with those of more traditional short-term memory paradigms, and reveal the suitability of the successive-matching procedure for studying memory processes.     

Pigeons' memory for number of events: Effects of intertrial interval and delay interval illumination

In Experiment 1, pigeons were trained at a 0-s baseline delay to discriminate sequences of light flashes (illumination of the feeder) that varied in number but not time (2f/4s and 8f/4s). During training, the intertrial interval was illuminated by the houselight for Group Light, but it was dark for Group Dark. Testing conducted with dark delay intervals produced a strong choose-small bias in both groups. All birds then received baseline training with a 5-s dark delay and were subsequently tested at shorter and longer dark delays. A choose-small bias was again observed at delays longer than the training delay, while a choose-large bias occurred at delays shorter than the training delay. Differentiating the ambient chamber illumination during the intertrial interval and the delay interval did not attenuate choose-small or choose-large effects. In Experiment 2, all birds received baseline training with a 5-s illuminated delay and were subsequently tested at shorter and longer illuminated delays. A choose-large bias was observed at delays longer than the training delay, while a choose-small bias occurred at delays shorter than the training delay. In Experiment 3, on intermittent test trials, when the duration of the second flash on small-sample trials was equal to the total flash duration on large-sample trials (i.e., 1600 ms), accuracy fell to approximately chance. These results suggest that pigeons discriminated the sequences of light flashes that varied in number but not in total duration of the sequence by relying on other temporal properties of the sequence rather than by using an event switch to count flashes.     

Massed versus distributed exposure and imaging of faces: Changing the test view

This research examined the effects of massed versus distributed exposure and imaging of faces, and the effects of changing the study-to-test view on subsequent recognition performance. The massed procedure consisted of individual faces exposed once for 6 s, followed by a 30 s off period. The distributed procedure consisted of faces exposed three times for 2 s, followed by a 10 s off period after each exposure. During the off periods, groups of participants either imaged the previous face, imaged another face, or performed an irrelevant letter-search task. Results showed that distributed exposure and post-exposure imaging of target faces facilitated recognition, but these effects primarily occurred when the same facial view was given at both study and test. Recognition diminished when the target was presented in a different view at test, but when combined with distributed presentation and target imaging, performance was enhanced. Implications for suspect identification and recognition of other kinds of complex visual stimuli are discussed.