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The role of preparation in overlapping-task performance.

We examined how performance of two overlapping discrete tasks is organized and controlled. Experiment 1 showed that when stimuli were presented in an unexpected order, expectations rather than actual presentation order determined the order in which the two stimuli were processed. In Experiment 2, when task order was unpredictable, performance was facilitated when task order was repeated on consecutive trials. In Experiment 3, performance of the second but not the first task benefited greatly when task order was held constant as compared to regularly alternated between trials; such effects were especially pronounced at short intertrial intervals. These results suggest that sequential performance of overlapping tasks is scheduled in advance and is regulated by initially allocating the central processing channel to one task and subsequently switching this channel to the other task.

Adult↗

Attentional tracking in the perception of apparent motion: evidence from sequential blanking displays.

Perception of sequential blanking displays was studied in a series of three experiments investigating factors that influence whether "shadow motion" or "item motion" is seen in a display. In addition to the duration of the blanking interval (BI) itself, three other such factors were identified: the eccentricity at which the display is viewed, the spacing of items in the display, and the type of motion that subjects are instructed to try to see. It is argued that these and other previously reported results are explicable without the need to invoke any kind of visual integration period. Instead, they are interpreted in terms of a first-order system of automatic luminance detectors and a second-order tracking system involving both voluntary and involuntary attention. The relationship of these findings to other recent work in apparent motion and visual attention and to other bistable motion displays is discussed.

Attention↗

Executive processes in visual and spatial working memory tasks.

Three experiments are reported, which have investigated the nature of the cognitive mechanisms that underlie performance on specific visuo-spatial working memory tasks, with the emphasis on exploring the extent of central executive involvement. Experiments 1 and 2 employed oral random digit generation as an executive task within a dual-task paradigm. The results of both experiments indicated that visuo-spatial tasks that involve sequential processing of information show more interference with random digit generation than do visuo-spatial tasks that involve simultaneous processing. The third experiment substituted oral random digit generation for executive tasks that did not involve memory for serial order (vigilance tasks adapted from Vandierendonck, De Vooght, & Van der Goten, 1998b). The results indicated significant interference between the vigilance tasks and the sequential visuo-spatial task, but not with the simultaneous visuo-spatial task. Overall the results of the three experiments are interpreted as indicating that serial sequential visuo-spatial tasks involve executive resources to a significantly greater extent than do simultaneous visuo-spatial tasks, and that this can have implications for studies that attempt to make use of such tasks to fractionate separable visual and spatial components within working memory.

Adolescent↗

How does running memory span work?

In running memory span, a list ends unpredictably, and the last few items are to be recalled. This task is of increasing importance in recent research. We argue that there are two very different strategies for performing running span tasks: a low-effort strategy in which items are passively held until the list ends, when retrieval into a capacity-limited store takes place; and a higher-effort strategy in which working memory is continually updated using rehearsal processes during the list presentation. In two experiments, we examine the roles of these two strategies and the consequences of two types of interference.

Analysis of Variance↗

The impact of path crossing on visuo-spatial serial memory: encoding or rehearsal effect?

The determinants of visuo-spatial serial memory have been the object of little research, despite early evidence that not all sequences are equally remembered. Recently, empirical evidence was reported indicating that the complexity of the path formed by the to-be-remembered locations impacted on recall performance, defined for example by the presence of crossings in the path formed by successive locations (Parmentier, Elford, & Maybery, 2005). In this study, we examined whether this effect reflects rehearsal or encoding processes. We examined the effect of a retention interval and spatial interference on the ordered recall of spatial sequences with and without path crossings. Path crossings decreased recall performance, as did a retention interval. In line with the encoding hypothesis, but in contrast with the rehearsal hypothesis, the effect of crossing was not affected by the retention interval nor by tapping. The possible nature of the impact of path crossing on encoding mechanisms is discussed.

Analysis of Variance↗

Short-term memory impairment and arithmetical ability.

We document the dissociation of preserved calculation skills in a patient with impaired auditory short-term memory. The patient (MRF) had a memory span of three digits. Furthermore, he showed rapid decrement in performance of single digits and letters with both auditory and visual presentation in the Brown-Peterson forgetting task. Analysis of his calculation skills revealed a normal ability to solve auditorily presented multidigit addition and subtraction problems such as 173 + 68 and to execute the Paced Auditory Serial Addition Task (Sampson, 1956, 1958; Gronwall, 1977). In addition, his performance on other tests, including arithmetic manipulation of natural numbers, decimals and fractions, approximation, magnitude, ratio, and percentage, appeared to be normal (Hitch, 1978b). It is argued that these findings require a revision of Baddeley and Hitch's (1974) concept of the function of working memory.

Amnesia↗

Direction of report in spatial and verbal serial short-term memory.

Four experiments examined the role played by item and order information in determining the effects of order of report of a sequence from short-term memory. Experiments in which list items were re-presented prior to recall so that only their order had to be reported showed no differences in performance between the forward and backward direction of report. This result was found with lists of auditory-verbal, visual-verbal, and spatial stimuli. When the list items were not re-presented, so that recall of both items and order was required, recall in the backward direction of report was significantly worse than in the forward direction of report, both in spatial and verbal tasks. The results point to the symmetry of inter-item associations, though only equivocally so, but they suggest strongly that the processes of spatial and verbal serial recall share many functional characteristics.

Adult↗

Serial order in spatial immediate memory.

Serial order effects in spatial memory are investigated in three experiments. In the first an analysis of errors in recall data suggested that immediate transpositions were the most common error and that order errors over 2 or 3 adjacent items accounted for the majority of errors in recall. The first and last serial positions are less error-prone than is the middle position in sets of six and seven items. A second experiment investigated recognition of transpositions and found that immediate transpositions were hardest to recognize but that a traditional serial position effect was not found. This may be due to the difficulty of maintaining one set of spatial items when another set is presented for comparison. A probe experiment, in which subjects were asked to recognize whether a single item came from a memory set and then to assign it to its position in the set indicated that the first and last positions were remembered more accurately than were central positions. The combination of serial order data in recall and position data suggests that there are similarities between serial order and position effects in the verbal and spatial domains and that serial order in spatial sequences is position-based.

Adult↗

Recency effect in Alzheimer's disease: a reappraisal.

This study investigated the hypothesis that discrepant results regarding the recency effect in Alzheimer's disease (AD) patients are due to the different scoring procedures used by various authors and/or to the different number of terminal items attributed to the recency part of the curve. Our results indicate that the last two processed words are available to AD patients for recall, just as they are to controls. Words processed slightly earlier are less available to AD patients than to controls, presumably because of the accelerated forgetting rate in demented patients.

Aged↗

Distribution of programming in a rapid aimed sequential movement.

Studies indicate that rapid sequential movements are preprogrammed and that preprogramming increases with complexity, but more complex sequences that require on-line programming have been seldom been studied. The purpose of this investigation was to determine whether on-line programming occurs in a 7-target sequence in which there is a unique target constraint and if so, to determine how different task constraints affect the distribution of additional programming. Subjects contacted seven targets with a hand-held stylus as quickly as possible while maintaining a 90% hit rate. Initiation-band execution-timing patterns and movement kinematics were measured to determine when the additional programming took place. Results indicated that additional programming occurred before initiation and during movement to the first target when the constraint required more spatial accuracy (small target). A different type of unique target (a triple hit of one target) caused the additional programming to occur on-line one or two segments before its execution. Different positions of the unique target also affected timing patterns. Results were discussed in terms of: (1) capacity of processing; (2) control of movement variance; and (3) mean velocity as a programmed parameter in sequential aiming movements.

Adult↗

Interfering with the central executive by means of a random interval repetition task.

Four dual-task experiments are reported in which a short-term memory task is performed concurrently with a random interval repetition task, which was designed to interfere with functions normally attributed to the central executive in the working memory model of Baddeley and Hitch (1974). The task was found to interfere with supra-span serial recall and with backward memory span, but did not disrupt performance on a forward-memory-span task. The effects were observed in dissociation with effects of articulatory suppression and matrix tapping, so that the locus of the effects of the new task is not due to the slave systems. In addition, single-task random-interval repetition performance was sampled and compared to performance in the dual-task conditions of all four experiments. Although quality of tapping performance differed between the single-task and the dual-task conditions, it was not related to recall performance. All the results are discussed with reference to the working memory model.

Adult↗

Increases in intrusion errors and working memory deficit of poor comprehenders.

This study tests the hypothesis that the ability to inhibit already processed and actually irrelevant information could influence performance in the listening span test (Daneman & Carpenter, 1980) and have a crucial role in reading comprehension. In two experiments, the listening span test and a new working memory test were given to two groups of young adults, poor and good comprehenders, matched for logical reasoning ability. In Experiment 1, the poor comprehenders had a significantly lower performance in the listening span test associated to a higher number of intrusions--that is, recalled words that, in spite of being in sentence form, were not placed in the last position. In Experiment 2, a new working memory test was devised in order to analyse more effectively the occurrence of intrusions. Subjects were required to listen to a growing series of strings of animal and non-animal words. While listening, they had to detect when an animal word occurred, and at the end of each series they had to recall the last word of each string. The poor comprehenders obtained a significantly lower performance in the memory task and made a higher number of intrusions, particularly of animal words.

Adult↗

Semantic similarity and immediate serial recall: is there a detrimental effect on order information?

Four experiments investigated the disruptive effect of semantic similarity on short-term ordered recall. Experiments 1 and 2 contrasted immediate serial recall performance for lists of semantically similar items, drawn from the same semantic category, with performance for lists that contained items from different categories. Experiments 1 and 2 showed the usual similarity advantage for item information recall, but, contrary to expectations, there was no similarity disadvantage for the recall of order information even when the level of item recall was controlled. Experiments 3 and 4 replicate and extend these findings by using an order reconstruction task or a limited word pool strategy, both of which yield alternate measures of order retention. These findings clearly contradict the wide spread belief stating that semantic similarity hinders the short-term recall of order information. Results are discussed in the light of a retrieval-based account where the effects of semantic similarity reflect the processes called upon at recall: It is suggested that long-term knowledge is accessed to support the interpretation of degraded phonological traces.

Adult↗

Is there a temporal basis of the word length effect? A response to Service (1998)

Service (1998) carried out a study of the word length effect with Finnish pseudowords in which short and long pseudowords were identical except for the inclusion of certain phonemes differing only in pronunciation length, a manipulation that is impossible in English. She obtained an effect of phonemic complexity but little or no word duration effect per se--a discrepancy from the expectations generated by the well-known working memory model of Baddeley (1986). In the present study using English words, we controlled for phonemic complexity differences by using the same words for the short- and long-word sets, but with instructions inducing shorter or longer pronunciation of the words. We obtained substantial word duration effects. Concerns raised by Service are addressed, and we conclude that both duration and complexity are likely to contribute to the word length effect in serial recall.

Adult↗

Individual differences in memory span: the contribution of rehearsal, access to lexical memory, and output speed.

Rehearsal speed has traditionally been seen to be the prime determinant of individual differences in memory span. Recent studies, in the main using young children as the subject population, have suggested other contributors to span performance, notably contributions from long-term memory and forgetting and retrieval processes occurring during recall. In the current research we explore individual differences in span with respect to measures of rehearsal, output time, and access to lexical memory. We replicate standard short-term phenomena; we show that the variables that influence children's span performance influence adult performance in the same way; and we show that lexical memory access appears to be a more potent source of individual differences in span than either rehearsal speed or output factors.

Adult↗

Rats' memory for serially presented novel flavours: evidence for non-spatial primacy effects.

Four experiments examined the effects of serially presenting a number of novel flavours to rats on their subsequent consumption of those flavours. In Experiments 1-4, rats were orally infused with 0.5 ml of flavour over 30 sec for each of five flavours in the exposure phase of the experiment. In these studies, primacy and recency effects emerged, the size of the primacy effect being related to the length of the retention interval, which varied from zero to twenty-four hours. Thus, both primacy and recency effects can be generated using non-spatial stimuli with rats.

Animals↗

Spatial imagery preserves temporal order.

Line drawings were presented in either a spatial or a nonspatial format. Subjects recalled each of four sets of 24 items in serial order. Amount recalled in the correct serial order and sequencing errors were scored. In Experiment 1 items appeared either in consecutive locations of a matrix or in one central location. Subjects who saw the items in different locations made fewer sequencing errors than those who saw each item in a central location, but serial recall levels for these two conditions did not differ. When items appeared in nonconsecutive locations in Experiment 2, the advantage of the spatial presentation on sequencing errors disappeared. Experiment 3 included conditions in which both the consecutive and nonconsecutive spatial formats were paired with retrieval cues that either did or did not indicate the sequence of locations in which the items had appeared. Spatial imagery aided sequencing when, and only when, the order of locations in which the stimuli appeared could be reconstructed at retrieval.

Cognition↗

Neuropsychological effects of risperidone in children with pervasive developmental disorders: a blinded discontinuation study.

OBJECTIVE: Little is known about the neuropsychological effects of risperidone in children with pervasive developmental disorders. METHOD: Twenty-four children (aged 5-17 years) with pervasive developmental disorders and co-morbid disruptive behavior who responded favorably to open-label treatment with risperidone as part of a previously described controlled discontinuation study completed two different computerized attention tasks at baseline, weeks 4, 8, and 24 of open-label treatment, and, at 8 weeks after random assignment to either placebo or risperidone. The primary efficacy measures were response latencies to visually presented stimuli requiring two different types of attention-controlled processing, i.e., focused and divided attention. RESULTS: About half of the clinical responders did not produce valid performance measures. These could be shown to be of younger mental age and less adaptive as measured by the Vineland Behavior Scales. For the valid task performers divided attention (serial search in working memory) was shown to regress in the placebo group (n = 7), while in the risperidone group (n = 7) there was further improvement. No such group difference was found for focused attention. CONCLUSIONS: The study suggests a beneficial effect of risperidone after several months of treatment, enhancing divided attention in children with pervasive developmental disorders.

Adolescent↗