The influence of theme identifiability

In the present study, we used the Deese/Roediger-McDermott paradigm to analyze the relationship between theme identifiability of word lists and false memories in adults and children. We conducted two normative studies to determine the identifiability levels for critical unpresented words in 40 associative lists in adults and in 16 associative lists in children. Then, in three experiments, false memories for critical words that were either easy or hard to identify were analyzed in adults and in children 4–5 years old and 11–12 years old. Opposite results were found for adults and children. Lists with highly identifiable critical words produced fewer false memories for adults but more false memories for children. These results suggest that, if they can identify critical words, adults use an identify-to-reject strategy to edit out false memories, whereas, in children, theme identification does not lead to the use of such a monitoring strategy.     

The influence of retrieval on retention

Four experiments tested the hypothesis that successful retrieval of an item from memory affects retention only because the retrieval provides an additional presentation of the target item. Two methods of learning paired associates were compared. In the pure study trial (pure ST condition) method, both items of a pair were presented simultaneously for study. In the test trial/study trial (TTST condition) method, subjects attempted to retrieve the response term during a period in which only the stimulus term was present (and the response term of the pair was presented after a 5-sec delay). Final retention of target items was tested with cued-recall tests. In Experiment 1, there was a reliable advantage in final testing for nonsense-syllable/number pairs in the TTST condition over pairs in the pure ST condition. In Experiment 2, the same result was obtained with Eskimo/English word pairs. This benefit of the TTST condition was not apparently different for final retrieval after 5 min or after 24 h. Experiments 3 and 4 ruled out two artifactual explanations of the TTST advantage observed in the first two experiments. Because performing a memory retrieval (TTST condition) led to better performance than pure study (pure ST condition), the results reject the hypothesis that a successful retrieval is beneficial only to the extent that it provides another study experience.     

The development of visual encoding and retention skills

The development of the ability to visually encode and maintain a visual stimulus was examined in a paradigm in which verbal encoding of the stimulus was prevented. The 8-, 12-, and 21-year-old subjects participated in a shadowing task during which they viewed a letter which was visually presented for 200 msec, 5 sec after the shadowing list began. On each trial subjects either reported the letter immediately after presentation or continued shadowing for 4 or 10 sec. Although results replicated those found in previous research using the paradigm, no age differences were found in recall accuracy, types of errors, or introspective reports describing perceived recall strategy. These findings suggest that even 8 year olds were able to employ a visual code and retain it for several seconds in a situation in which incentive to do so was provided.     

The effect of encoding time on retention by infants and young children

Using a Visual Recognition Memory (VRM) procedure, we examined the effect of encoding time on retention by 1- and 4-year olds. Irrespective of age, shorter familiarization time reduced retention, and longer familiarization time prolonged retention. The amount of familiarization that yielded retention after a given delay decreased as a function of age.     

The influence of attention on holistic face encoding

We examined the influence of attention on the formation of holistic face representations using the composite effect (Perception 16 (1987) 747). In Experiment 1, stimuli composed of a face superimposed on a house were shown during encoding. Subjects delineated either the face or the house, thus manipulating attention away or toward the face. In Experiment 2, an intact face image was presented with letters scrolling from top to bottom. Subjects were asked to either ignore the letters or read them and decipher the words that they formed. Aligned and misaligned composites were shown at testing. Recognition performance was consistently better for misaligned than aligned stimuli, regardless of the allocation of attention during encoding. In Experiment 3, we show that the composite effect can be eliminated by a disruption in holistic processing at the time of encoding. We conclude that holistic encoding is one aspect of face analysis that occurs equally well with or without attention.     

The influence of partial reinforcement on serial autoshaping with pigeons

The effect of partial reinforcement on the rate of responding during the first element of a serial compound was investigated using autoshaping in pigeons. Experiment I employed the illumination of a response key by two different colours as the elements of the compound. Responding during the first element was faster when this stimulus was intermittently paired with the second element and the unconditioned stimulus than when a continuous reinforcement schedule was employed. Experiment II demonstrated that this effect of partial reinforcement is unaffected by maniuplating the associative strength of the second element at the outset of compound conditioning. A similar effect of partial reinforcement was also found in Experiment III which used a tone as the first element of the serial compound.     

Perceptual identification and encoding

Sequences containing 10 numbers from 1–20 were presented in serial-order or random-order at rates of 1/sec, 2/sec, and 4/sec for serial-order or same-orderrecall by eight Ss. Stimulus duration was constant, so that the interpresentation interval decreased as rate of presentation increased. Serial-order recall was greater for serial-order presentation than for random-order presentation. The decrease in recall as presentation rate increased was similar for both serial-order and random-order presentation. This result indicates that serial-order recall of random-order presentation does not involve reordering or repeated sequential scanning. It is consistent with the view that serial-order recall of serial-order presentation is greater because identification time is decreased. due to the decrease in the range of relevant alternatives, so that increased encoding time results in storage of more information.     

The influence of acoustic similarity on serial recall of letter sequences

Acoustic similarity is known to impair short-term memory (STM) for letter sequences. The present series of experiments investigated the effects of acoustic similarity on long-term retention. In the first experiment, subjects were asked to learn one of two lists of 8 letters, the letters being either of high or low acoustic similarity. Lists were visually presented for three trials, with subjects responding after each trial. Then subjects participated in an immediate memory task for digits which lasted for 20 min. Finally, subjects tried to recall the list of letters they had learned previously. Lists having items of high acoustic similarity were more difficult to recall on the first trial, but were better recalled on the delayed retention test. In a second experiment, groups of subjects were again asked to learn one of two lists of 8 letters differing in acoustic similarity, using different orders of the letters used previously. The procedures were identical except that in two groups, a STM task for digits intervened between the presentation and test of the letters. This intervening task minimized the effects of STM and eliminated the differences in retention found previously. In a third experiment, better long-term retention for material having high acoustic similarity was also obtained when subjects used a backward recall procedure. In the last experiment 14 item lists were learned to a criterion of two correct trials, and retention was tested after each trial and at a delay of 20 min. and 23 hr. No effect of acoustic similarity was found and little retention loss occurred. These results suggest that reducing the STM component by introducing a STM control or by lengthening the list caused the effect of acoustic similarity to disappear.     

The reference frame for encoding and retention of motion depends on stimulus set size

The goal of this study was to investigate the reference frames used in perceptual encoding and storage of visual motion information. In our experiments, observers viewed multiple moving objects and reported the direction of motion of a randomly selected item. Using a vector-decomposition technique, we computed performance during smooth pursuit with respect to a spatiotopic (nonretinotopic) and to a retinotopic component and compared them with performance during fixation, which served as the baseline. For the stimulus encoding stage, which precedes memory, we found that the reference frame depends on the stimulus set size. For a single moving target, the spatiotopic reference frame had the most significant contribution with some additional contribution from the retinotopic reference frame. When the number of items increased (Set Sizes 3 to 7), the spatiotopic reference frame was able to account for the performance. Finally, when the number of items became larger than 7, the distinction between reference frames vanished. We interpret this finding as a switch to a more abstract nonmetric encoding of motion direction. We found that the retinotopic reference frame was not used in memory. Taken together with other studies, our results suggest that, whereas a retinotopic reference frame may be employed for controlling eye movements, perception and memory use primarily nonretinotopic reference frames. Furthermore, the use of nonretinotopic reference frames appears to be capacity limited. In the case of complex stimuli, the visual system may use perceptual grouping in order to simplify the complexity of stimuli or resort to a nonmetric abstract coding of motion information.     

The influence of visual symmetry on the encoding of objects

Two experiments examined how symmetry affects the visual encoding of simple flat objects (lamellae). Experiment 1 showed that subjects encode a lamella's shape as both a facsimile and its enantiomorph. In Experiment 2 the errors made when responding to symmetrical and asymmetrical stimuli showed that there were three factors affecting the reproduction of a symmetrical stimulus. These are, in order of decreasing influence, (i) the orientation of the axis of symmetry, (ii) the presence of overall symmetry (irrespective of orientation), and (iii) identity of the orientation of the elements of the response in relation to those of the stimulus. They also show that symmetry is likely to be reproduced even where the reproduction is not of the same shape as the original stimulus. The relevance of these results to representation of objects is discussed.     

Temporal aspects of retrieval in short-term serial retention

In three experiments, temporal properties of memory retrieval are studied. Latency of positionally probed recall of a single item is measured as a function of its serial position (SP) in a serial list. The requested SP is indicated by a positional probe, presented immediately after the list. For two organizational structures of the list (i.e., grouped vs. ungrouped lists) the experiments study the effects of precueing the probe position briefly before probe presentation, the cue signal indicating the SPs relevant for recall. The problem of confounded effects on latency of requested SP and of probe-signal location is also investigated. A bow-shaped SP-curve is found for ungrouped lists; precueing reduces RT but does not affect the bowed shape. This argues against selective confounding effects of spatial probe position and also suggests that precueing preactivates memory access. Grouping the items into two sublists eliminates precueing effects for items around the group boundary. Furthermore, precueing is detrimental when SPs at opposite ends of the list are precued. This suggests that the available points of memory access can only be utilized one at a time, so that precueing is not beneficial when the item cannot be reached via the preactivated point. Although the notion of single access to memory is in accord with both positional cueing theory and non-associative hierarchical theories (e.g., Estes 1972), various details of the results are in favor of the first type of explanation.     

The influence of camera angle on comprehension and retention of pictorial events

A subset of formal compositional principles was examined in the context of narrative pictorial events. Slide stories were constructed of six common events in which characters were depicted from three camera angles: low angle, eye-level, and high angle. After presentation, subjects evaluated the characters, recalled the stories, and engaged in a recognition task. Camera angle influenced subjects’ evaluation and retention of the stories in accordance with aesthetic principles. Camera angle had significant, predictable effects on judgments of the physical and personal characteristics of the characters, on recall of these characteristics, and on recall of the gist of the stories themselves. Recognition memory for camera angle was significantly less accurate than recognition memory for the characters. Subjects used the available visual information to construct coherent story representations, and, although camera angle strongly influenced the construction of these representations, specific camera angle information became less accessible.     

The effects of forced serial processing on identification of words and random letter strings

Skilled readers identified words and random letter strings displayed one letter at a time on the screen of a computer-controlled oscilloscope. Letters were either displayed in a single position, or painted left-to-right in adjacent positions. Adjacent displays were either unmasked, masked by a letter-like pattern following each letter (backward masking) or masked by a pattern preceding each letter (forward masking). Unmasked words were identified with a high degree of accuracy, and accuracy was independent of the exposure duration of the letters over the range 50–200 msec. Masked adjacent word displays and one-position word displays were identified much less accurately, and accuracy was highly dependent on letter exposure duration. In contrast to these results, identification of random strings, or of letters within random strings, was almost unaffected by the presence of the mask and was dependent on letter exposure duration under all display conditions. The results are interpreted as evidence that (a) masking forces subjects to process serial displays one letter at a time, and (b) words, or large segments of words, are habitually processed in parallel, while random strings are processed as a series of individual letters or small chunks.     

The influence of sleep deprivation and knowledge of results on perceptual encoding

This study investigates the way sleep deprivation effects on perceptual processes are modulated by knowledge of results (KR). In a choice-reaction task, signal quality was manipulated, combined with and without KR and under increasing levels of lack of sleep. It was found that the decrease of performance due to sleep deprivation was larger when stimuli were degraded. KR counteracted the effect of sleep deprivation; however, KR improved performance irrespective of signal quality. Hence, sleep deprivation seems to have a twofold effect on performance; one effect on perceptual processing, which is insensitive to KR, and another effect on some different processing stage, which is sensitive to KR. The results were interpreted in terms of a model of human performance (Sanders 1983) in which a distinction is made between two energetical mechanisms, ‘arousal’ and ‘activation’, subserving perceptual and motor stages of information processing, respectively. Thus, KR appears to compensate for the deficiency of one type of energetical mechanism, caused by sleep deprivation. Yet, this compensation does not appear to be the result of increased arousal, because, irrespective of KR, the performance decrement caused by signal degradation was more pronounced with lack of sleep.     

An investigation of serial learning and retention processes in children

Three studies investigated both serial learning (SL) and retention processes among first through sixth graders. SL processes were evaluated for both pictorial and verbal materials by use of a probing methodology, and retention processes were studied as a function of the amount of intratask interference during original learning. All three SL stimuli considered (prior item, serial position, and prior-item cluster) were found to be functional, although the prior-item stimulus was most frequently used. Additionally, SL rate was found to improve with increasing age. The introduction of interference into SL through acoustic, associative, or semantic similarity facilitated retention in control as well as proactive and retroactive inhibition conditions. Pictorial serial list items improved SL performance only for second, third, and fourth graders, while fifth graders performed better with verbal materials and sixth-grade performance was comparable in both presentation modes.