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.     

Determinants of pigeons' waiting time: Effects of interreinforcement interval and food delay

Four pigeons performed on three types of schedules at short (i.e., 10, 30, or 60 s) interreinforcement intervals: (a) a delay-dependent schedule where interreinforcement interval was held constant (i.e., increases in waiting time decreased food delay), (b) an interreinforcement-interval-dependent schedule where food delay was held constant (i.e., increases in waiting time increased interreinforcement interval), and (c) a both-dependent schedule where increases in waiting time produced increases in interreinforcement interval but decreases in food delay. Waiting times were typically longer under the delay-dependent schedules than under the interreinforcement-interval-dependent schedules. Those under both-dependent schedules for 1 subject were intermediate between those under the other two schedule types, whereas for the other subjects waiting times under the both-dependent procedure were similar either to those under the delay-dependent schedule or to those under the interreinforcement-interval-dependent schedule, depending both on the subject and the interreinforcement interval. These results indicate that neither the interreinforcement interval nor food delay is the primary variable controlling waiting time, but rather that the two interact in a complex manner to determine waiting times.     

Short-term retention of pictures and words as a function of type of distraction and length of delay interval

Picture and word triads were tested in a Brown-Peterson short-term retention task at varying delay intervals (3, 10, or 30 sec) and under acoustic and simultaneous acoustic and visual distraction. Pictures were superior to words at all delay intervals under single acoustic distraction. Dual distraction consistently reduced picture retention while simultaneously facilitating word retention. The results were interpreted in terms of the dual coding hypothesis with modality-specific interference effects in the visual and acoustic processing systems. The differential effects of dual distraction were related to the introduction of visual interference and differential levels of functional acoustic interference across dual and single distraction tasks. The latter was supported by a constant 2/1 ratio in the backward counting rates of the acoustic vs. dual distraction tasks. The results further suggest that retention may not depend on total processing load of the distraction task, per se, but rather that processing load operates within modalities.     

Fixed interval schedules and delay of reinforcement

In a fixed interval schedule of reinforcement the only responses to be reinforced are those made when a certain time interval has elapsed since the previous reinforcement. The behaviour of three rats on such a schedule was compared with their behaviour on a schedule where a response made at any time during the interval was reinforced by setting up a reward which was delivered when the interval had elapsed. Response rates were higher in the ordinary fixed interval schedule than in its modified version, and it is argued that this rules out attempts to explain the maintenance of fixed interval performance by delayed reinforcement. Despite the clear difference in response rates, there was considerable similarity between the post-reinforcement pauses developed in the two schedules, and this suggests that pausing is influenced more by temporal than by response contingencies.     

The length of the retention interval,forgetting, and subjective similarity

A long retention interval tends to result in the poor retention known as forgetting. A high subjective similarity between stimuli frequently produces their poor retention. Thus, a long retention interval may increase the subjective similarity between stimuli (the RIISS hypothesis), and this increase may produce forgetting. To examine this hypothesis, college students made speeded same-different discriminations between two lines or tones of different lengths or frequencies that were 400 ms or 3,300 ms apart, and they rated the similarity of these stimuli. The long interval produced poorer overall performance as expected, but also produced poorer performance on different than same stimuli, implying that it increased the subjective similarity between the initial and subsequent stimuli, and it also increased rated similarity, in support of the RIISS hypothesis. The position that stored stimuli lose less common information than distinctive information explains RIISS evidence better than does perturbation theory.     

Children's memory of events: effects of stress,age, time delay and location of interview

To examine the ability of children aged between 4 and 12 years to recall a stressful event (venipuncture) compared with a non-stressful event (demonstration of venipuncture), recall was tested after 6–8 weeks. Half also had recall tested after 2–7 days. Testing took place where the stressful event occurred (n=122) or at a neutral location (n=127). Children who experienced the stressful event were less likely to give inaccurate responses in free recall or to acquiesce to suggestive misleading questions. Apart from incorrect responses in free recall, correct responses increased and incorrect responses decreased with increasing age. Recall after 2–7 days was superior to recall after 6–8 weeks. Those who had an early and a late interview had better recall at the late interview than those who had a late interview only. The location of interview showed no effects on recall. © 1998 John Wiley & Sons, Ltd.     

Fixed-interval performance: The dynamics of behavior and the interval length

Postreinforcement pauses from successive intervals under various fixed-interval schedules (ranging from 15 seconds to 480 seconds in length) were subjected to lag-1 autocorrelation analysis. Results from both rats and pigeons suggested that there was a consistent tendency for pause values in successive intervals to be weakly positively related. This tendency did not appear to change systematically with interval length and was exhibited both when the reinforcer magnitude was constant and when it was variable at different interval values. The findings do not support suggestions that the dynamic properties of performance under fixed-interval schedules vary systematically with interval length, and are in the opposite direction from some previous findings suggesting that measures of behavior (such as post-reinforcement pause length or number of responses) in successive intervals are inversely related.     

Lexical decision in sentences: Effects of syntactic structure

A lexical decision paradigm was used to examine syntactic influence on word recognition in sentences. Initial fragments of sentences were presented visually (CRT display) one word at a time (at reading speeds), from left to right. The string terminated with the appearance of a lexical decision target. The grammatical structure of the incomplete sentence affected lexical decision reaction time (RT). In Experiment 1, modal verb contexts followed by main verb targets and preposition contexts followed by noun targets produced lower RTs than did the opposite pairings (i.e., modal/noun and preposition/verb). In Experiment 2, transitive verb contexts followed by noun targets and subject noun phrase contexts followed by verb targets yielded lower RTs than did the opposite pairings. Similar contrasts for adjective targets did not yield comparable effects in Experiment 2, but did when the adjective was the head of a predictable phrase (Experiment 4). In Experiment 3, noun targets yielded lower RTs than did verb targets after contexts of a transitive verb followed by a prepositional phrase. An account of these effects is offered in terms of parsing constraints on phrasal categories.     

Effects of syntactic expectations on speech segmentation

Although the effect of acoustic cues on speech segmentation has been extensively investigated, the role of higher order information (e.g., syntax) has received less attention. Here, the authors examined whether syntactic expectations based on subject-verb agreement have an effect on segmentation and whether they do so despite conflicting acoustic cues. Although participants detected target words faster in phrases containing adequate acoustic cues ("spins" in take spins and "pins" in takes pins), this acoustic effect was suppressed when the phrases were appended to a plural context (those women take spins/*takes pins [with the asterisk indicating a syntactically unacceptable parse]). The syntactically congruent target ("spins") was detected faster regardless of the acoustics. However, a singular context (that woman *take spins/takes pins) had no effect on segmentation, and the results resembled those of the neutral phrases. Subsequent experiments showed that the discrepancy was due to the relative time course of syntactic expectations and acoustics cues. Taken together, the data suggest that syntactic knowledge can facilitate segmentation but that its effect is substantially attenuated if conflicting acoustic cues are encountered before full realization of the syntactic constraint.     

Children's reactions to failure as a function of interresponse interval

Several studies have reported that nonreward facilitates subsequent performance; other studies have found that failure is followed by a performance decrement. Experiments that have shown facilitating effects of nonreward have used interresponse intervals of at least 5 sec, whereas those that have shown decremental effects of failure have used 0-sec interresponse intervals. The present study examined the effects of .5-, 1.0- and 5.0-sec interresponse intervals on children's lever-pulling responses following success and failure on a ball tower task. Second- and third-grade children responded slower following failure relative to success with .5- and 1.0-sec interresponse intervals. Speeds following success and failure did not differ when the interresponse interval was 5.0 sec. Increases in interresponse interval were associated with increases in speeds following failure, but speeds following success were not related to interresponse interval. These results were discussed in terms of frustration-produced competing responses and Elliott (1970) analysis of the influence of preparatory intervals on children's reaction-time performance.     

Schedule-induced polydipsia as a function of fixed interval length

Rats were trained to bar-press for Noyes pellets on an FI schedule which was increased serially through several values from 2 sec to as high as 300 sec. Concurrently, water was freely available. As FI length was increased, the degree of polydipsia increased linearly to a maximum value.     

Stroboscope motion: Effects of duration and interval1

The quality of stroboscope motion induced by the successive presentation of two illuminated squares obeys two rules. For all stimulus durations shorter than 100 msec, optimal motion occurs when the stimulus onsets differ by about 120 msec. For stimulus durations longer than 100 msec, optimal motion occurs when the second stimulus begins at the termination of the first stimulus. The two rules relating quality of motion to duration suggest a single principle, namely, that the quality depends only on the interval between the visual responses to the two stimuli. The interresponse interval at which motion is optimal is independent of stimulus duration.