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PubMed1996

Working memory: activation limitations on retrieval.

Two experiments which require subjects to hold a digit span while solving an equation and then recall the digit span are performed. The size of the memory span and the complexity of the equation are manipulated as well as whether the subject is required to substitute items from the digit span for constants in the equation. As either task (digit span recall or equation solving) gets more complex there are performance decrements (accuracy or latency) not only in that task but also in the other task. It is also shown that the majority of the errors are misretrievals. These results are consistent with the proposal that working memory load has its impact on retrieval from memory. These results are fit by the ACT-R theory (Anderson, 1993) which assumes that there is a limit on source activation and that this activation has to be divided between the two tasks. As either task increases in complexity there is less activation for retrieval of information from declarative memory. Subjects' misretrievals of associatively related information could be predicted by assuming a partial matching process in ACT-R.

Adult↗
PubMed1993

Prevalence of abnormal neurobehavioral scores in populations exposed to different industrial chemicals.

The aim of the study is to establish the prevalence of neurobehavioral scores of occupationally exposed subjects below the 10th percentile rank of normalized curves obtained on a referent population. The Milan Automated Neurobehavioral System (MANS) was administered to 400 drivers from public and private firms; their data were distributed on the basis of age and years of school attendance and were normalized by determining percentile rank equivalence. The exposed population is made up of 20 lead- and zinc-exposed subjects, 18 welders exposed to aluminum for less than 1 year, 150 exposed to different metals in the ferromanganese production, 73 lithographic operators exposed to gasoline and petroleum, 197 exposed to solvents mixtures in the paint manufacture, and 23 dropouts of the same firm. The percentages of scores below 10th percentile rank were calculated in the different exposure groups and in the different age-school attendance ranges. The prevalence of results below the 10th percentile rank was found to be related to the intensity of the exposures and to the low levels of school attendance. In the 20-29 and the 30-39 age ranges, there was a prevalence of POMS scale scores below 10th percentile rank, in the 50-59 age range, the percentages were high for the Digit Symbol, the mean value of Simple Reaction Time, Serial Digit Learning, and Benton Visual Recognition.

Adult↗
PubMed1997

Serial recall of poor readers in two presentation modalities: combined effects of phonological similarity and word length.

Immediate ordered memory for words in poor readers was compared with that of two control groups of normal readers, matched on chronological age and reading age, respectively. The groups were equated for basal memory capacity. Phonological similarity and word length were simultaneously manipulated. Items were presented either auditorily (spoken words) or visually (their corresponding drawings). The results suggest that when having to recall a restricted set of items and when verbal output is eliminated, phonological coding and rehearsal occur to the same extent in poor and normal readers, with auditory as well as visual presentation. However, irrespective of presentation modality, absolute performance of the poor readers was still worse than that of their chronological age controls.

Adolescent↗
PubMed1997

Phonological skill and articulation time independently contribute to the development of memory span.

One hundred twenty 6- to 10-year-olds were administered three measures of speed of processing, three memory span tasks, three tasks assessing phonological skill, and three articulation tasks assessing the speed with which they could say familiar stimuli aloud. Regression analyses revealed that performance on the span tasks was predicted by performance on the phonology and articulation tasks but not by age or performance on the processing speed tasks. Results are discussed in terms of the processes responsible for age-related change in memory span.

Child↗
PubMed1999

Infants' memory processing of a serial list: list length effects.

Six-month-olds, trained with a three-mobile serial list, exhibit a primacy effect 24 h later. In three experiments, we demonstrated that increasing list length impairs their memory for serial order. In all experiments, 6-month-olds were trained with a five-mobile list. In Experiment 1, infants failed to exhibit a primacy effect on a 24-h delayed recognition test, recognizing mobiles from all serial positions. In Experiment 2, infants did exhibit a primacy effect on a reactivation (priming) test, suggesting that they may originally have encoded serial-order information. Experiment 3 confirmed that serial-order information was represented in infants' training memory. After the reactivation treatment, infants were precued with one list member and tested for recognition of another. When precues specified valid order information, infants recognized test mobiles from the later serial positions. The memory dissociation for serial order on delayed recognition and reactivation tests adds to the growing evidence that young infants possess two functionally distinct memory systems.

Analysis of Variance↗
PubMed2000

Persistence of memory for ignored lists of digits: areas of developmental constancy and change.

Contrary to the common belief that sensory memory remains unchanged across development in childhood, there have been several previous reports suggesting that the persistence of sensory memory, at least for sounds, increases with age in childhood. Because those previous studies all used isolated sounds as stimuli, it is not yet clear how this developmental difference influences the recall of sound series. The present study adapts the procedure of J. S. Saults and N. Cowan (1996), who studied memory for attended and ignored spoken words, to examine here the recall of attended and ignored lists of digit. A developmental increase in the persistence of memory was obtained only for the final item in an ignored list, which is the item for which sensory memory is thought to be the most vivid at short retention intervals.

Adult↗
PubMed2000

The effect of switching between sequential and repetitive movements on cortical activation.

We used whole-head functional magnetic resonance imaging (fMRI) to investigate the effect of switching between different sequential and repetitive movements in the context of conditional and fixed tasks. Four different movement tasks were applied: (1) unpredictable switching between two movement sequences comprising six submovements each according to visual cues (SEQ-VC); (2) unpredictable switching between repetitive movement of one finger according to visual cues (REP-VC); (3) performance of the same sequential movements used for SEQ-VC but in a fixed mode triggered by a visual stimulus (SEQ-FIX); (4) performance of the repetitive movements used for REP-FIX but in a fixed mode by a visual stimulus (REP-FIX). The statistical group analysis of the hemodynamic responses revealed the following results: (1) the SEQ-VC compared to the SEQ-FIX condition (switching between movement sequences) engendered stronger activations in the left rostral supplementary motor area (pre-SMA), bilaterally in the posterior parietal lobule, the left ventral premotor area, and the visual cortices; (2) the REP-VC compared to the REP-FIX condition (switching between repetitive movements) only revealed stronger activation in extra-striate areas. We hypothesize that during switching of movement sequences higher motor control aspects are involved including movement selection, updating of motor plans, as well as recalling and restoring motor plans. The repetitive movements are too simple in order to evoke additional activations in the medial and lateral premotor areas, as well as in parietal areas.

Adult↗
PubMed2001

Differential working memory load effects after mild traumatic brain injury.

The objective of this study was to explore the effects of increasing working memory (WM) processing load on previously observed abnormalities in activation of WM circuitry shortly after mild traumatic brain injury (MTBI). Brain activation patterns in response to increasing WM processing load (auditory n-back: 0-, 1-, 2-, and 3-back conditions) were assessed with fMRI in 18 MTBI patients within 1 month of their injury and in 12 healthy controls. Performance accuracy on these tasks was also measured. Brain activation patterns differed between MTBI patients and controls in response to increasing WM processing loads. Controls maintained their ability to increase activation in regions of WM circuitry with each increase in WM processing load. MTBI patients showed disproportionately increased activation during the moderate processing load condition, but very little increase in activation associated with the highest processing load condition. Task performance did not differ significantly between groups on any task condition. MTBI patients showed a different pattern of allocation of processing resources associated with a high processing load condition compared to healthy controls, despite similar task performance. This suggests that injury-related changes in ability to activate or modulate WM processing resources might underlie some of the memory complaints after MTBI.

Adolescent↗
PubMed2001

Prefrontal contributions to executive control: fMRI evidence for functional distinctions within lateral Prefrontal cortex.

The prefrontal cortex (PFC) plays a fundamental role in internally guided behavior. Although it is generally accepted that PFC subserves working memory and executive control operations, it remains unclear whether the subregions within lateral PFC support distinct executive control processes. An event-related fMRI study was implemented to test the hypothesis that ventrolateral and dorsolateral PFC are functionally distinct, as well as to assess whether functional specialization exists within ventrolateral PFC. Participants performed two executive control tasks that differed in the types of control processes required. During rote rehearsal, participants covertly rehearsed three words in the order presented, thus requiring phonological access and maintenance. During elaborative rehearsal, participants made semantic comparisons between three words held in working memory, reordering them from least to most desirable. Thus, in addition to maintenance, elaborative rehearsal required goal-relevant coding of items in working memory ("monitoring") and selection from among the items to implement their reordering. Results revealed that left posterior ventrolateral PFC was active during performance of both tasks, whereas right dorsolateral PFC was differentially engaged during elaborative rehearsal. The temporal characteristics of the hemodynamic responses further suggested that dorsolateral activation lagged ventrolateral activation. Finally, differential activation patterns were observed within left ventrolateral PFC, distinguishing between posterior and anterior regions. These data suggest that anatomically separable subregions within lateral PFC may be functionally distinct and are consistent with models that posit a hierarchical relationship between dorsolateral and ventrolateral regions such that the former monitors and selects goal-relevant representations being maintained by the latter.

Adolescent↗
PubMed2002

Predicting perceptual events activates corresponding motor schemes in lateral premotor cortex: an fMRI study.

The ability to recognize sequential patterns of external events enables us to predict their future course and thus to plan and execute actions based on current perceptions and previous experiences. Here we show with functional magnetic resonance imaging that even in the absence of movement the prediction of sequential patterns activates brain areas involved in the representation of specific motor schemas. Particularly, the prediction of size engages premotor areas involved in hand movements (superior part of the ventrolateral premotor cortex), whereas the prediction of pitch engages premotor areas involved in articulation (inferior most ventrolateral premotor cortex). The findings indicate that events are mapped onto somatotopically corresponding motor schemes whenever we predict sequential perceptions.

Adult↗
PubMed2002

Dissociable executive functions in the dynamic control of behavior: inhibition, error detection, and correction.

The present study employed event-related fMRI and EEG to investigate the biological basis of the cognitive control of behavior. Using a GO/NOGO task optimized to produce response inhibitions, frequent commission errors, and the opportunity for subsequent behavioral correction, we identified distinct cortical areas associated with each of these specific executive processes. Two cortical systems, one involving right prefrontal and parietal areas and the second regions of the cingulate, underlay inhibitory control. The involvement of these two systems was predicated upon the difficulty or urgency of the inhibition and each was employed to different extents by high- and low-absent-minded subjects. Errors were associated with medial activation incorporating the anterior cingulate and pre-SMA while behavioral alteration subsequent to errors was associated with both the anterior cingulate and the left prefrontal cortex. Furthermore, the EEG data demonstrated that successful response inhibition depended upon the timely activation of cortical areas as predicted by race models of response selection. The results highlight how higher cognitive functions responsible for behavioral control can result from the dynamic interplay of distinct cortical systems.

Adult↗
PubMed1993

The effect of temporal and force changes on the patterning of sequential movements.

This article examines the programming of relatively long sequences of action with the control of sequential movements being effected through the use of a tapping task involving a sequence of five taps. Subjects were required to tap with their right hand at rates of 150, 200, and 250 ms. There were two conditions, with subjects being required either to increase, in condition 1, or to decrease, in condition 2, the force at one of the five tap positions (all five tap positions were examined), then return to the previous force level. Changes in timing resulting from variations in the force characteristics have previously been discussed in terms of changes in the organizational time required (Semjen, Garcia-Colera, & Requin, 1984). The current study breaks the intertap interval down into two separate components: the contact interval (finger in contact with the key) and the non-contact interval (interval preceding the tap). Although changes in the non-contact interval could be explained in terms of changes in the organizational time required, changes in the contact interval appeared to be a result of the mechanical changes in force.

Adolescent↗
PubMed1993

Central and peripheral coordination in movement sequences.

Motor coordination has been too poorly defined to be a useful construct in studying the control of movement. In general, motor coordination involves controlling both the timing and the kinematics of movement. Yet the motor behaviors typically used for the study of coordination have required controlling only the timing or the spatial aspects of a movement. To understand better the basis of motor behavior, this study examined movement sequences, a class of movement in which both the timing and the kinematics must be controlled. In one experiment we studied a reaching and grasping movement sequence to characterize the central coordination of movement sequences. In another experiment we studied a throwing movement sequence to characterize the peripheral (kinesthetic) coordination of movement sequences. An heuristic model is presented to explain how central and peripheral mechanisms of coordination might interact to produce accurate movement.

Adolescent↗
PubMed1997

Reverse "repetition blindness" and release from "repetition blindness": constructive variations on the "repetition blindness" effect.

N. Kanwisher observed that subjects shown rapid lists of words recall two occurrences of a repeated word less often than two unrelated words. Kanwisher explained this "repetition blindness" through a type/token account, which assumes that encoding the second occurrence of a repeated word is inhibited if it occurs too soon after the first. More fundamentally, it assumes that failure to recall a word from a rapid list results from failure to encode its occurrence. Contrary to that interpretation, we observed that subjects can often recognize words that they cannot recall from a rapid list. We also observed "reverse repetition blindness," when the second presentation was given greater contextual support, and a "release from repetition blindness" effect, when distinctive contextual support was given to ech occurrence. We concluded that a constructive account of remembering provides a better explanation of all of the effects.

Adult↗
PubMed1996

Action planning during the presentation of stimulus sequences: effects of compatible and incompatible stimuli.

Experimental designs that require the simultaneous perception and reproduction of a stimulus sequence could help to clarify the relationship between perception and action. This contribution examines a specific stimulus-response compatibility with the reproduction of simple stimulus sequences. In the procedure a response just prepared or one to be prepared is confronted with a new incoming stimulus that is compatible or incompatible with the response. Interference is predicted from a framework in which stimulus perception and action control are assumed to share common codes. Five arrows were successively presented at 1-s intervals. The arrows pointed either to the left or to the right with equal probability. One of the five arrows was accompanied by a randomly presented go signal. Subjects then had to reproduce the sequence by pressing corresponding left or right keys while the stimulus presentation continued. Reaction-time latencies and reaction intervals within a sequence were analyzed in six experiments. Results showed increasing reaction-time latencies the later the go signal was presented--that is, the longer the sequence to be reproduced was. In contrast to previous findings, this effect interacted with the compatibility between the arrow displayed together with the go signal and the first reaction. It is argued that the go signal initiates a transfer of a cognitive action plan to a peripheral motor program and that this process is subject to interference the more the current stimulus is at odds with one of the first parameter specification.

Adult↗
PubMed1996

The effect of enactment on memory for order.

The effect of enactment on memory for serial order was investigated in two experiments. In both experiments a reconstruction task was used to separate order from item information. In Experiment 1 enactment and test information was manipulated between groups. For subjects who had not been informed about the reconstruction test, performance of verbal and motor groups was similar with regard to both serial-position curves and overall performance. For subjects who knew beforehand that they would be tested for memory of the order of the action events, performance in the verbal condition was significantly better than in the motor condition. In Experiment 2, the reversed enactment effect for test-informed subjects was replicated with a within-subjects design. The results agree with Engelkamp and Zimmer's (1984, 1994) position that enactment serves exclusively to enhance item information, and indicate that subjects have less control over the encoding processes when they are enacting than during verbal encoding (cf. Cohen, 1981).

Adult↗
PubMed1979

Plasma levels of d-amphetamine in hyperactive children. Serial behavior and motor responses.

Amphetamine has been clearly documented to be an efficacious treatment for hyperactive children. The pharmacokinetics of amphetamine have been studied in adults, but not in children. Sixteen male children who scored greater than 2SD from norms on Factors I and IV of Conner's Teacher Rating Scale and who were not excluded for reasons to do with medical or psychiatric conditions, intelligence, or age, had a plasma d-amphetamine apparent elimination half-life of 6.8 +/- 0.5h. Peak plasma level occurred between 3 and 4h (62.7 +/- 3.8 and 65.9 +/- 3.6 ng/ml, respectively). Six of these children had a repeat study and there were no significant differences within subject in apparent elimination half-lives and attained peak blood levels. The variation in plasma levels was greater during absorption than during elimination. Both behavioral and motor activity responses as analyzed by differences between amphetamine and placebo days (by paired t-tests) indicate significant responses between hours 1--4; however, these responses do not correlate with plasma amphetamine levels; they occur during the absorption phase. The decreased response to later similar plasma levels of d-amphetamine may be related to depletion of catecholamine stores, to replacement by a 'false neurotransmitter' metabolite of amphetamine, or to alteration in receptor sensitivity.

Child↗