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PubMed2003

Automatic mediation or absence of mediation? Commentary on Crutcher and Ericsson (2000).

R. J. Crutcher and K. A. Ericsson (2000; see record 2000-05419-014) showed that subjects stopped reporting mnemonic mediation in a recall task after sufficient practice. They concluded that subjects continued to use the mediator indefinitely but that its execution eventually became automatic and no longer required access to working memory. Their article thus supports the more general hypothesis that multistep cognition can take place without awareness. In this article the authors evaluate that conclusion on both conceptual and empirical grounds and report results of a new experiment that indicate that a qualitative shift to direct, unmediated recall can occur for at least some tasks.

Attention↗

PubMed2005

Dissociation of neural systems mediating shifts in behavioral response and cognitive set.

The ability to generate appropriate behaviors in response to changing situations requires both the alteration of ongoing behavior and the understanding of the global rules governing stimulus categorization in a given context. Neuropsychological tests that have been developed to measure this form of cognitive flexibility, such as the Wisconsin Card Sorting Test, have reliably demonstrated that individuals with lesions in regions of the prefrontal cortex and basal ganglia have difficulty generating a cognitive set and altering rule-governed behavior. Recent neuroimaging studies have supported the role of these brain regions in the performance of response shifting and cognitive set shifting. However, the precise role of these regions in the individual components of these tasks remains a contentious issue. Here, we used event-related functional magnetic resonance imaging (fMRI) to dissociate the neural circuitry involved in the alteration of ongoing behavior and the shifting of cognitive set. Participants viewed geometric shapes as they appeared individually in rapid succession and responded with an appropriate button press based upon whether the individual shape was a predetermined target stimulus. Responses were required for each shape presented. The fMRI results indicated that response shifting specifically activated a dorsal neural circuit comprised of the dorsolateral prefrontal cortex, anterior cingulate, and intraparietal sulcus. Shifts in cognitive set were mediated by ventrolateral prefrontal cortex, anterior cingulate, and striatum. These findings suggest that the alteration of ongoing behavior and shifting of cognitive set are mediated by two distinct neural systems interconnected by the anterior cingulate.

Adult↗

PubMed1999

Egocentric frame of reference: its role in spatial bias after right hemisphere lesions.

The reference shift hypothesis of unilateral neglect holds that spatial bias in left neglect stems from a rightward deviation of patients' egocentric frame of reference (ER). Twenty five unselected right brain-damaged patients participated in a straight-ahead pointing task to assess the position of their ER (Experiment 1). A rightward ER shift emerged only in the subgroup of patients with extensive parietal lesions. In Experiment 2, we found that the position of the ER did not predict the outcome of various visuospatial neglect tests (r = 0.07 to 0.27). In Experiment 3, no significant positive correlation emerged between the ER position and visual (r = 0.26) or tactile (r = -0.48) extinction. Two further experiments examined the relationships between the ER position and patients' performance on a reaction time test of directional motor bias (Experiment 4), and on a test of response times to lateralised visual stimuli (Experiment 5). Results showed that the ER position did not predict the distribution of accuracy scores or response times in either task (Experiment 3: accuracy: r = 0.06; response times: r = 0.16; Experiment 4: accuracy: r = 0.09; response times: r = 0.04). We concluded that the position of the ER plays no crucial role in the behavioural consequences of spatial bias induced by right hemisphere lesions.

Aged↗

PubMed1989

Shifts in hemispheric advantage during familiarization with complex visual patterns.

Twenty females unfamiliar with kanji were given a recognition task involving tachistoscopic presentation of kanji to the right and left visual fields. Repeated exposure to these novel stimuli resulted in significantly increased competence at the task. To analyze different approaches to the task, subjects were divided into an initial left visual field advantage and an initial right visual field advantage group. Over the course of the experiment subjects in the initial left visual field advantage group shifted from a left to a right visual field advantage, showing both a linear trend and a quadratic trend, while the initial right visual field advantage group showed only a quadratic trend. The results are consistent with observations in other novel stimuli situations which have demonstrated a shift in hemispheric advantage from right to left with increased competence and which have demonstrated individual differences in the pattern of shifting hemispheric advantage.

Adult↗

PubMed2000

High-speed memory scanning: a behavioral argument for a serial oscillatory model.

In order to account for the memory span [G.A. Miller, The magical number seven, plus minus two: some limits on our capacity for processing information, Psychol. Rev. 63 (1956) 81-97.], the magical number seven, plus minus two, and high-speed scanning in human memory ¿S. Sternberg, High speed scanning in human memory, Science 153 (1966) 652-654., Lisman and collaborators [O. Jensen, J.E. Lisman, An oscillatory short-term memory buffer model can account for data on the Sternberg task, J. Neurosci. 18 (1998) 10688-10699; J.E. Lisman, M.A.P. Idiart, Storage of 7+/-2 short-term memories in oscillatory subcycles, Science 267 (1995), 1512-1515.] proposed an oscillatory short-term memory buffer model. In this neurophysiological model: "a single brain network can separately maintain up to seven memories by a multiplexing mechanism that uses theta and gamma brain oscillations for clocking. A memory is represented by groups of neurons that fire in the same gamma cycle" ¿O. Jensen, J.E. Lisman, An oscillatory short-term memory buffer model can account for data on the Sternberg task, J. Neurosci. 18 (1998) 10688-10699, p. 10688. To test this model, we tried to modify the memory scanning time by shifting the gamma oscillation frequency. To this aim, we replicated the visual short-term memory scanning task ¿S. Sternberg, High speed scanning in human memory, Science 153 (1966) 652-654., and we simultaneously used the protocol that Treisman ¿M. Treisman, A. Faulkner, P.L.N. Naish, D. Brogan, The internal clock: evidence for a temporal oscillator underlying time perception with some estimates of its characteristics frequency, Perception 19 (1990) 705-743. designed to drive, slowing down or speeding up, a temporal oscillator acting in the gamma range ¿J.G.R. Jefferys, R.D. Traub, M.A. Whittington, Neuronal networks for induced "40 Hz rhythms, Trends Neurosci. 19 (1996) 202-208; W. MacKay, Synchronized neuronal oscillations and their role in motor processes, Trends Cog. Sci. 1 (1997) 176-183; M. Treisman, N. Cook, P.L.N. Naish, J.K. MacCrone, The internal clock: electroencephalographic evidence for oscillatory processes underlying time perception, Q. J. Exp. Psychol. 47A (1994) 241-289.. In this protocol, an auditory periodic stimulus (click train) was delivered at various frequencies during the task. The reaction time (RT), the slope, and the intercept of the linear function associating RT to memorized list length showed systematic modulations according to the stimulation frequency. The predicted driving effects due to the click trains were obtained, consisting of localised modulations of performance on the stimulation frequency band. We argue that memory scanning is indeed paced by a temporal oscillator, thus providing behavioral arguments for the serial oscillatory model of Lisman.

Adult↗

PubMed2005

Effects of mental fatigue on attention: an ERP study.

The effects of mental fatigue on attention were assessed. Subjects performed a visual attention task for 3 h without rest. Subjective levels of fatigue, performance measures and EEG were recorded. Subjective fatigue ratings, as well as theta and lower-alpha EEG band power increased, suggesting that the 3 h of task performance resulted in an increase in fatigue. Reaction times, misses and false alarms increased with time on task, indicating decreased performance efficiency in fatigued subjects. Subjects were unable to inhibit automatic shifting of attention to irrelevant stimuli, reflected by a larger negativity in the N1 latency range for irrelevant, compared to relevant stimuli. This difference in negativity was unaffected by time on task. However, N1 and N2b amplitude did change with time on task: N1 amplitude decreased, and the difference in N2b amplitude between relevant and irrelevant stimuli (larger N2b amplitude evoked by relevant stimuli) decreased with time on task. The results indicate a dissociation in the effects of mental fatigue on goal-directed (top-down) and stimulus-driven (bottom-up) attention: mental fatigue results in a reduction in goal-directed attention, leaving subjects performing in a more stimulus-driven fashion.

Adolescent↗

PubMed1991

An interleaved tracking procedure to monitor unstable psychometric functions.

In some experimental situations, the psychometric function underlying performance may not be stable, but instead may shift along the stimulus axis in response to changes in attention, learning, or task difficulty. When this occurs, the measured threshold may be influenced and the slope of the measured function will be inaccurately shallow. With commonly used experimental procedures, it is difficult to know whether a shallow psychometric function slope is a true reflection of the sensory process, or is a result of "averaging" a highly variable underlying function. Here, a new method is described of estimating psychometric function slope from the variability in two interleaved adaptive tracks, consulted on alternate trials, that is resistant to the effects of shifting performance levels. Further, a mechanism is described for assessing the likelihood that a threshold was, in fact, stable over the course of its measurement. Computer simulations are reported as well as verification of the method in measurements of human performance on a psychophysical task. Several conditions of externally imposed variability were simulated to establish the ability of these procedures to identify unstable functions and produce accurate slope estimates. The procedures worked well for thresholds shifting by as little as 4 dB if the variation did not occur too rapidly. The procedure and associated analyses are recommended as a relatively "free" means of calculating slope and quantifying threshold reliability with little extra experimental effort.

Attention↗

PubMed1989

Attentional shift towards the rightmost stimuli in patients with left visual neglect.

In a search task where four letters were displayed to the right of a central fixation point, right brain-damaged patients with visual neglect showed the fastest response when the target was at the rightmost position and progressively slower responses as it moved towards the center of the display. This finding confirms Kinsbourne's claim that in visual neglect an important role is played by the magnetic attraction that the extreme end of the right structured space exerts on the patient's attention.

Adult↗

PubMed2002

Psychological and physical stress-induced cardiovascular reactivity and diurnal blood pressure variation in women with different work shifts.

There is increasing evidence that diurnal blood pressure (BP) variation, in addition to high BP per se, is related to target organ damage and the incidence of cardiovascular events. However, the determinants of diurnal BP variation are not adequately understood. This paper tests the hypothesis that cardiovascular reactivity to acute stress and/or delayed recovery predicts greater diurnal BP variation (i.e., a lower sleep/awake BP ratio). We studied the relationship of diurnal BP variation (assessed by ambulatory BP monitoring) to mental stress (mental arithmetic and anger recall tasks) and physical stress (treadmill)-induced cardiovascular reactivity and recovery in 87 female nurses who worked different shifts. The sleep/awake systolic BP (SBP) ratio was negatively correlated with relative SBP reactivity (maximum SBP increase/baseline SBP: r = -0.21, p = 0.06) and relative stress response (average of SBP during stress/baseline SBP:r = -0.23, p = 0.04) induced by anger recall, while the correlations of the sleep/awake SBP ratio with other parameters of reactivity or recovery in the anger recall or mental arithmetic task were not significant. When subjects were divided into day-shift workers (n=54) and night-shift workers (n = 33), the sleep/awake SBP ratio was negatively correlated with relative SBP reactivity (r = -0.41, p = 0.02) and relative stress response of SBP (r = -0.48, p = 0.006) induced by anger recall, and positively correlated with recovery rate (r = 0.34, p = 0.06) in the latter group, while these correlations were not significant in the former group. The sleep/awake SBP ratio was inversely correlated with the exercise-induced SBP increase in the day-shift workers (r = -0.30, p = 0.03), while this association was not found in the night-shift workers. In conclusion, cardiovascular reactivity triggered by psychological and physical stress in the laboratory may be a weak, but significant, determinant of diurnal BP variation; in addition, work shift (day or night) appears to moderate the relationship between these two pressor mechanisms.

Adult↗

PubMed1991

Shifting visual attention and selecting motor responses: distinct attentional mechanisms.

Does shifting visual attention require the same central mechanism as that required for selecting overt motor responses? In Experiment 1, Ss performed 2 tasks: a speeded manual response to a tone and an unspeeded report of a cued target letter in a brief masked array. Stimulus onset asynchrony (SOA) between tone and array was varied. If the attention shift to the target was delayed by the first task, then there should be more second-task errors at short SOAs and on trials with slow first-task responses. In fact, SOA effects and dependencies were minimal. Results were unchanged in further experiments in which the relation between cue and target was symbolic, spatially "unnatural," or based on the color of the target. Two additional experiments validated key assumptions of the method. The results confirm that although selection of motor responses constitutes a processing bottleneck, the control of visual attention operates independently of this bottleneck.

Adult↗

PubMed1994

PET studies of parietal involvement in spatial attention: comparison of different task types.

Five experiments are described that concern the mechanisms that direct attention to spatial and non-spatial features of a stimulus and the effects that attention has on the visual system's analysis of that stimulus. Shifts of attention from one spatial location to another activated the superior parietal lobe and this activation was fairly independent of the task performed on the attended object, the response made to the attended object, and whether the shift of attention was controlled endogenously or exogenously. Maintaining attention tonically on a location or a particular visual feature such as shape, colour or motion did not produce a superior parietal response. Tonic attention to a feature (colour, shape, motion) or location, however, did produce enhancements in the response of various regions that are probably specialized for processing the attended visual feature. The activation of superior parietal cortex during shifts of spatial attention as well as the activation of parietal-occipital cortex when attention is tonically maintained on a location suggest that the parietal cortex plays an important role in spatial computations.

Animals↗

PubMed2002

Late plasticity for language in a child's non-dominant hemisphere: a pre- and post-surgery fMRI study.

The ability of the right hemisphere to sustain the acquisition or the recovery of language after extensive damage to the left hemisphere has been essentially related to the age at the time of injury. Better language abilities are acquired when the insult occurs in early childhood (perinatal insults) compared with later occurrence. However, while previous studies have described the neuropsychological pattern of language development in typical cases, the neural bases of such plasticity remain unexplored. Non-invasive functional MRI (fMRI) is a unique tool to assess the neural correlates of brain plasticity through repeated studies, but the technique has not been widely used in children because of methodological limitations. Plasticity of language was studied in a boy who developed intractable epilepsy related to Rasmussen's syndrome of the left hemisphere at age 5 years 6 months, after normal language acquisition. The first fMRI study at age 6 years 10 months showed left lateralization of language networks during a word fluency task. After left hemispherotomy at age 9 years, the child experienced profound aphasia and alexia, with rapid recovery of receptive language but slower and incomplete recovery of expressive language and reading. Postoperative fMRI at age 10 years 6 months showed a shift of language-related networks to the right during expressive and receptive tasks. Right activation was seen mainly in regions that could not be detected preoperatively, but mirrored those previously found in the left hemisphere (inferior frontal, temporal and parietal cortex), suggesting reorganization in a pre-existing bilateral network. In addition, neuropsychological data of this case support the hypothesis of innately more bilateral distribution of receptive than expressive language. This first serial fMRI study illustrates the great plasticity of the child's brain and the ability of the right hemisphere to take over some expressive language functions, even at a relatively late age. It also suggests a limit for removal of the dominant hemisphere beyond the age of 6 years, a classical limit for the critical period of language acquisition.

Brain↗

PubMed2006

TIPS (trigger an IIF paradigm shift).

CHALLENGE: New Mexico Corporate Services (NMCS) recordable injuries have been averaging 2-4 per year for the last 5 years with no statistical improvement. However, we believe all NM employees must go home incident and injury free every day and just as healthy as they came to work. In addition, we have received feedback from several sources, that indicates some employees are reluctant to report injuries. These indicators showed us that continuing our current strategies, making incremental improvement and changes, would not give us the improvement desired. We needed a paradigm shift to get everyone completely engaged in the IIF (Incident & Injury Free) culture, in order to achieve true IIF results. METHODS/STRATEGIES: We formed a small (3-person) taskforce consisting of safety representatives from EHS, Site Services and CS Operations. We reviewed 5 years worth of data to determine what was injuring our people. We also decided to review all injuries, not simply those classified as recordable by OSHA standards. First we identified the types of injury information needed to get a true picture of our safety issues. We analyzed IRB (Incident Review Board) data showing us the following factors and whether any of them contributed to the injury: - Date - Incident Description - Severity - Root Cause - Type of Injury - Season - Work Group/Shift - Area - Improper evaluation of hazard - Inadequate work procedures - Incorrect Mental Model - Inadequate PPE Requirement - Failure to Follow or Unaware of PPE Requirement - Shortcut or Schedule Pressure - Last or First Day of Shift or Adjacent to Holiday - OT - Aggravate Existing Condition - Inadequate Training or Passdown - Experience in Task - Corrective Action Taken - Overall Quality of Response. Once this information was collected for all injuries in an Excel file, we graphed it several ways to help reveal trends: Shift 7 had double the injuries of shift 5. Night shift injuries were relatively high but lower than Shift 7. Shift 5 had no severe (recordable) injuries. Biggest total injury type was ergonomic. Biggest recordable injury type (58%) was cuts/lacerations. Chemical exposure and inhalations resulted in no recordables. Biggest root cause category was behavioral. Biggest behavioral root cause was "Failure to Evaluate Hazards". Biggest administrative controls root cause was "Inadequate Procedures". Biggest engineering controls root cause was "Unrecognized Workplace Hazard". Majority of injuries occurred in Spring/Summer which accounted for 86% of recordables. Response was inadequate or poor for 25% of injuries. Number of injuries by workgroup were about equal. Work area injuries were mostly in the CUB and Subfab but CUB injuries favored cuts/lacerations while Subfab favored ergonomic injuries. These learnings and gaps were used to develop our New Mexico Site Safety Action Plan for 2005. It has also been used by individual managers and supervisors in their day-to-day business meetings, activities, and communications, for a more focused IIF message and effort. RESULTS: [graph: see text]. CONCLUSIONS/RECOMMENDATIONS: Challenges are different amongst shifts. Shift culture may be stronger than workgroup culture. Work areas pose different challenges that all should be aware of and prepared for. We should prepare ourselves for challenges posed by the Spring and Summer seasons as well. We should be aware of and prepare for the different challenges and cultures characteristic of each shift. Supervisors need to spend more time in the field with their people to help them address safety issues and help make IIF a more consistent component of daily workgroup culture. Each site should analyze their data and look for their unique safety challenges. This will allow customized, focused action plans that meet the unique needs of each site.

Accidents, Occupational↗

PubMed1994

Selective memory impairments produced by transient lidocaine-induced lesions of the nucleus accumbens in rats.

Reversible lidocaine-induced lesions of the nucleus accumbens (N.Acc.) impaired performance on the spatial win-shift, but not on the cued win-stay, radial arm maze task. Pretraining lesions on the former task did not affect foraging for 4 pellets during either the training or test phases. In contrast, lesions given prior to the test phase significantly disrupted retrieval of 4 pellets on the 8-arm maze. Comparable deficits also were observed in rats trained to forage for 4 pellets on an 8-arm maze without prior win-shift experience. State-dependent drug effects were ruled out by replicating the disruptive effects of lidocaine infusions into the N.Acc. on spatial win-shift performance in rats receiving this treatment prior to both training and test phases. These results suggest that the N.Acc. may interact with the hippocampus to guide foraging behavior requiring memory of previous spatial locations on a maze.

Animals↗

PubMed2001

Spatial deployment of attention within and across hemifields in an auditory task.

Research on visual attention has demonstrated that covert attention can be focused on particular locations within one hemifield, but that a specific "meridian" cost may also be found for shifting attention between hemifields. These issues have received less consideration for audition, even though reliable behavioral measures for the effects of spatial attention on hearing are now available. We examined the spatial distribution of covert attention in an auditory task following spatially non-predictive peripheral auditory cues (which should induce exogenous attention shifts), or following symbolic central cues that predicted the likely location for the auditory target (to induce endogenous attention shifts). In both cases, we found that attention can be focused not only on one hemifield versus another, but also within one hemifield in an auditory task. However, there was no unequivocal evidence for a meridian effect in audition.

Adult↗

PubMedDate not supplied

[Changes in the components of the human visual evoked potential during conditioning using biological feedback].

The VEPs to checkerboard-flashes were recorded from Cz in 32 healthy adult volunteers (14 men, 18 women) under biofeedback conditions. The subjects were instructed to modify N100-P200 component in such a way that the amplitude of the segment within selected time-window from the beginning of the sample to its main positive peak exceeded the definite threshold. Each subject solved the task by means of individual combination of voltage and temporal regulation with the prevalence of the latter. Shifts of the latencies both of N100 and P200 were involved in VEP modifications. Four groups of subjects were distinguished by their success in task performance which depended on the strategy and level of self-estimated tiredness. The latency of N300 (out of the chosen time-sample) was longer for the subjects which were successful in increasing the number of "correct" responses. Differences in VEP components depended on the strategy types, levels of self-estimated tiredness, and sex on the subjects.

Adult↗

PubMed2005

Control of attention in schizophrenia.

The deficits of attention contribute significantly to the clinical picture of functional disability seen in schizophrenia, but there is no consensus as to whether this cognitive function can be fractionated to allow further characterisation of the impairment. We examined fifteen patients with chronic schizophrenia and fifteen controls using paired tasks designed to measure four hypothetical aspects of attentional control: the ability to focus attention, to resist distraction, to shift attention, and to divide attention. The group with schizophrenia showed a significant improvement in accuracy on a digit span repetition task when a simultaneous box-crossing task was added (divided attention condition). Although the patient group showed impaired performance across nearly all of the tasks, they were not disproportionately impaired during the task conditions assumed to demand greater attention. These results suggest that the aspects of attention and executive function under study are not significantly affected by schizophrenia and indicate the need for further characterisation of the impairment usually reported using conventional tests of attention on those with schizophrenia.

Adult↗

PubMed2004

Straight-ahead pointing correlates with long-line bisection in neglect patients.

The spatial bias of neglect patients has been assumed to result from the alteration of a body-centred representation which underlies actions within personal and extra-personal spaces. This deficit seems to correspond to the ipsilesional deviation of the subjective straight-ahead (SSA), often described in neglect patients. However, several recent studies have failed to show significant correlations between the SSA deviation and performance in standard visuo-spatial tests of neglect. Since methodological choices could explain these negative results, the present study re-investigated the question. SSA, assessed by manual pointing, was anchored by instructions to a precise median body part. A body-centred line bisection task was also carried out, during the same session and in similar experimental conditions. Sixteen right brain-damaged patients with (n = 8) or without (n = 8) neglect, and 8 control subjects free of any neurological problem were included. Taken as a group, the neglect group stood out from the others in both tasks. Moreover, in neglect patients only, SSA position significantly correlated with bisection error for long lines, even if dissociations between SSA shift and bisection error were found in two cases. Results are discussed with regard to the nature of the tasks proposed in the different studies and to methodological aspects that could at least partly explain the aforementioned failures.

Adult↗