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PubMed1990

Schizophrenic performance on line bisection: no simple lateralization defects.

Many studies have assessed the possible lateralization deficits of schizophrenics, and the results usually suggest left hemisphere dysfunction. Nevertheless, they have been variable. This may have been due to cognitive demand of the different tasks, not to changes in brain lateralization itself. In order to circumvent this problem, the present study evaluates the performance of schizophrenics on a simple but lateralized task, line bisection. Subjects bisected a line using either visual or tactile information, with the left or right hand, when it was placed in their left or right hemispace or directly in front of them. Schizophrenic subjects were not more erroneous than normals (variable error), nor were they biased differently from normals in either direction with either modality of sensory input (constant error). There were only two significant effects of group on the tactile line bisection, one of position x length x group and one of position x hand x end x length x group, both on constant error (directional bias). The lack of main effects and presence of interactions on these basic tasks suggests that apparent lateralization differences found in schizophrenic subjects are due not to a simple defect of brain lateralization but may stem from task demands and attention allocation.

Attention↗
PubMed1997

The effects of frontal cortical lesions on remembering depend on the procedural demands of tasks performed in the radial arm maze.

We trained 24 rats to perform an eight-arm radial maze task and then assigned them with a matching procedure to one of three treatments: sham surgery or lesions of the projection areas of the mediodorsal thalamic nucleus (MDn) in the medial wall (MW) or in both the MW and rhinal sulcal (RS) areas of frontal cortex. After recovery we trained the rats to perform six tasks, beginning with the standard eight-arm task, followed by two versions of a four forced choice procedure, and then three versions of a two-choice delayed-nonmatching-to-sample (DNMTS) task. The two lesion groups performed comparably on all tasks, showing that impairments were not exacerbated by extension of the MW lesion to include all cortical areas innervated by MDn. As in previous studies, frontal animals performed the radial maze task poorly immediately after surgery but improved with subsequent training. Controlling the order of the arm entries by opening the first four gates in a random sequence had little effect on performance, although frontal animals were impaired when lengthy delays (5 or 15 min) were imposed after the last of the four forced entries. Frontal animals were not impaired on two-choice DNMTS when the arms used for training were selected at random from the eight alternatives on a trial by trial basis, even when visual cues were eliminated by darkening the room and covering the maze. Frontal animals were significantly impaired when the selection of sample and choice arms was limited to the same two alternatives on every trial. This finding may explain the reported sensitivity of DNMTS to the effects of frontal lesions when training is carried out in operant chambers.

Animals↗
PubMed1999

The usefulness of partial information: effects of go probability in the choice/Nogo task.

In the present study, we examined whether the use of partial information for response preparation depends on the utility of that partial information for meeting task demands. Using a choice/Nogo task, the utility of the partial information was varied by manipulating the proportion of Go relative to Nogo signals, and preliminary response preparation was indexed by the degree of lateralized readiness potential (LRP) activity on Nogo trials. The Nogo LRP was clearly present when Go probability was high (67% Go) and, to a lesser extent, when Go and Nogo signals were equiprobable. However, the Nogo LRP disappeared when the probability of a Go signal was low (25% Go). This pattern of results supports the hypothesis that response preparation will be based on partial stimulus information only when the information has significant utility in the context of the overall task requirements.

Adult↗
PubMed1981

Type A components and psychophysiological responses to an attention-demanding performance task.

Although Type A and B individuals appear to differ in psychophysiological responsivity, situations eliciting these differences have not been specified. The current experiment parametrically manipulated response speed in order to examine differences between behavior types in psychophysiological responsivity to this variable. Cardiovascular responses and performance in this paced task were compared to those from a task performed without explicit speed pacing in 24 businessmen classified as Type A or not. Only Type A businessmen showed a well-developed heart rate response in the self-paced task. In the experimenter paced task, the heart rate response of Type A's was most consistent when paced at fast response times; that of non-A's was most consistent when paced at relatively slow response times. Businessmen high in the Speed/Impatience component of Type A initiated anticipatory heart rate slowing later than non-A's and recovered less promptly. Overall relative to non-A's, A's appear to become readily involved and physiologically responsive to a task. Once involved, their responding is altered most by requirements for anticipation and relatively slow controlled response.

Arrhythmias, Cardiac↗
PubMed1989

Spatial monitoring in visual working memory.

Three experiments examined the role of spatial monitoring in short-term visual memory. In the first experiment it was found that with consonants presented visually at one location articulatory suppression but not a concurrent tracking task disrupted performance. Experiment 2 demonstrated that tracking was disruptive when consonants were presented at three locations and more serial positions were affected when the locations of the consonants were random rather than highly predictable. Articulatory suppression was also disruptive in this study. The third experiment replicated the first two studies, without an articulatory suppression condition, using a within-subject design with a strictly forward serial recall constraint. The locus of the tracking effect was modified by this recall constraint suggesting that tracking disrupts a specific process that utilizes spatial monitoring. It was concluded that spatial monitoring depletes resources that can be used to encode visually presented consonants and these resources may be drawn from spatial working memory. The articulatory loop was also implicated given that articulatory suppression also disrupted performance. These results were explained in terms of working memory constellations. Morris (1986 b) suggested that such constellations consist of working memory components, in this instance the articulatory loop and spatial working memory, 'assembled' to meet task demands. This probably involves the activation, by the demand characteristics of the task, of modules in working memory that are similar to production system elements.

Adult↗
PubMed1994

Topographical analysis of cortical evoked activity during a variable demand spatial processing task.

This experiment studied changes in brain activity as subjects performed a variable demand spatial rotation task. The task involved the sequential presentation of a template histogram and a spatially rotated comparison histogram. Task difficulty was manipulated by varying the number of bars and the degree of rotation. Topographical analysis of the brain event-related activity data indicated the presence of negative components that were maximal at the vertex within 80 ms and bilaterally in the temporal lobes within 140 ms of stimulus onset and that appeared to be insensitive to changes in task difficulty. Demand-sensitive potentials were recorded, however. Positive components corresponding to P200 and P300 activity were recorded symmetrically around site PZ. The P200 component declined in amplitude, but showed no changes in latency as task demand increased. P300 activity declined in both amplitude and latency as the task became more difficult. Finally, a positive component was recorded over right central cortex approximately 490 ms after stimulus onset. This component declined in amplitude but increased in latency as task difficulty increased.

Adult↗
PubMed1999

Does over-accomodation occur when using aircraft head-up displays?

BACKGROUND: Whether over-accommodation is caused by the use of head-up displays is still under debate. Most prior experimentation has involved cognitively demanding tasks, which are known to affect the accommodation response. The simulations have often been unrealistic and involved short working distances. HYPOTHESIS: Over-accommodation is caused not by the presence of a head-up display per se, but rather by the cognitive demand of the task. METHODS: The effect of increasing the task cognitive load and the use of forward looking infra-red imagery (FLIR) on the ocular accommodative response and task performance was assessed with a realistic head-up display assisted flying task. FLIR increases cognitive load due to its poor resolution and the need for interpretation of the images. RESULTS: Over-accommodation was found to be small in magnitude (0.17+/-0.03D; range -0.02-0.45D) occurring only with cognitively demanding tasks and with forward looking infrared imagery. Response times to detect tanks in the outside world scene were slower with increased cognitive load and forward looking infra-red imagery, along with a reduced detection rate, decreased accuracy of tracking tanks in the outside world and poorer control of the head-up display pitch ladder. When discrimination was added to detection in an outside world task, decisions were delayed until they could be accurately made, rather than performance degraded. CONCLUSION: The use of a virtual head-up display in a simulated aircraft environment did not adversely affect ocular accommodation. However, increased cognitive demand or FLIR imagery caused significant inward shifts of accommodation.

Accommodation, Ocular↗
PubMedDate not supplied

Cardiovascular and neuroendocrine responses to extended laboratory challenge.

The purpose of this study was to examine the effects of a 2-hour laboratory challenge on heart rate, blood pressure, catecholamines, and cortisol; and investigate the contribution of the physical act of speaking on both neuroendocrine and cardiovascular measures. Using a within-subjects design, 14 subjects were tested individually during two separate laboratory sessions. During one session, subjects engaged in two cognitively demanding tasks for 2 hours. During the other session, subjects executed the verbal demands of the tasks for 2 hours, but cognitive demands were absent. During both sessions, blood pressure and heart rate were measured and arterialized blood samples were obtained for the measurement of epinephrine, norepinephrine, and cortisol. Subjects demonstrated significantly greater increases in systolic blood pressure diastolic blood pressure, heart rate, epinephrine, and cortisol during the cognitively challenging session than during the control session. It is concluded that sustained elevations in cardiovascular and neuroendocrine measures can be achieved in the laboratory, and that the effects of such tasks cannot be attributed solely to the physical demands of speaking. Implications for the measurement of circulating catecholamines and cortisol during laboratory studies are discussed.

Adult↗
PubMed2003

No interference of task complexity with circadian rhythmicity in a constant routine protocol.

Time course in task performance has been studied extensively. In particular, the investigation of circadian rhythmicity in task performance that varied in complexity. However, these studies disclosed heterogeneous outcomes. This could be the result of confounding exogenous factors, the use of diverse tasks, as well as accumulating sleepiness interfering with the underlying circadian drive. The present study varied task demands systematically within a single task and a dual task, using a constant routine protocol to examine the unmasked influence of the endogenous circadian oscillator on the periodicity of performance. Moreover, the subjects were divided into an early-start and a late-start group to estimate the potential interaction of circadian rhythmicity with the duration of prior wakefulness. The results revealed a distinct congruence in the circadian rhythms of all performance measures, with which prior wakefulness (< 40 h) did not interact. Also, single-task as well as dual-task complexity did not interfere with circadian rhythmicity. In conclusion, when sufficiently controlled for masking exogenous factors, task complexity is removed from the underlying circadian rhythms.

Adult↗
PubMed2001

Discriminative whisking in the head-fixed rat: optoelectronic monitoring during tactile detection and discrimination tasks.

We compared whisking movement patterns during acquisition of tactile detection and object discrimination under conditions in which (a) head movements are excluded and (b) exposure to tactile discriminanda is confined to the large, moveable vibrissae (macrovibrissae). We used optoelectronic instrumentation to track the movements of an individual whisker with high spatio-temporal resolution and a testing paradigm, which allowed us to dissociate performance on an "indicator" response (lever pressing) from the rat's "observing" responses (discriminative whisking). We analyzed the relation between discrimination performance and whisking movement patterns in order to clarify the process by which the indicator response comes under the stimulus control of information acquired by the rat's whisking behavior. Whisking patterns over the course of task acquisition differed with task demands. Acquisition of the Detection task was correlated with modulation of only one whisking movement parameter-total number of whisks emitted, and more whisking was seen on trials in which the discriminandum was absent. Discrimination between a sphere and cube differing in size and texture was correlated with a reduction in whisk duration and protraction amplitude and with a shift towards higher whisking frequencies. Our findings confirm previous reports that acquisition of tactile discriminations involves modulation by the animal of both the amount and the type of whisking. In contrast with a previous report (Brecht et al., 1997), they indicate that rats can solve tactile object detection and discrimination tasks (a) using only the large, motile mystacial vibrissae (macrovibrissae) and (b) without engaging in head movements. We conclude that the functional contribution of the macrovibrissae will vary with the nature of the task and the conditions of testing.

Animals↗
PubMedDate not supplied

Verbal and figural recognition memory: task development and age associations.

The goal of the present study was to develop and validate parallel tests of verbal and figural delayed-recognition memory with similar task demands and difficulty levels. Such tasks would allow examination of age differences and longitudinal age changes in visual recognition memory for two types of stimuli, activate divergent neural systems, and allow us to use the same procedures within the confines of functional neuroimaging as those we use in standard neuropsychological administration. The tasks introduced here include a delay between target presentation and test phase, are matched in difficulty, and yield moderate levels of performance. Individual and group differences in task performance were examined in 80 cognitively normal men and women in two older age groups: 60 to 69 and 70 to 85. Accuracy averaged 74% in both tasks, with lower performance in the oldest age group. Although accuracy was equivalent between tasks, subjects had a more liberal response bias in the figural than verbal task. Performance on the new recognition-memory tests was significantly related to Benton Visual Retention Test (BVRT; Benton [1963]. New York: The Psychological Corporation) and California Verbal Learning Test (CVLT; Delis, Kramer, Kaplan, & Ober [1987]. New York: The Psychological Corporation) performance measures. The absence of floor or ceiling effects, wide range of individual variability, and demonstrated concurrent validity of the present tasks suggest their potential utility in functional neuroimaging studies and in the early detection of cognitive decline.

Acoustic Stimulation↗
PubMed1995

The N400 as a function of the level of processing.

In a semantic priming paradigm, the effects of different levels of processing on the N400 were assessed by changing the task demands. In the lexical decision task, subjects had to discriminate between words and nonwords, and in the physical task, subjects had to discriminate between uppercase and lowercase letters. The proportion of related versus unrelated word pairs differed between conditions. A lexicality test on reaction times demonstrated that the physical task was performed nonlexically. Moreover, a semantic priming reaction time effect was obtained only in the lexical decision task. The level of processing clearly affected the event-related potentials. An N400 priming effect was only observed in the lexical decision task. In contrast, in the physical task a P300 effect was observed for either related or unrelated targets, depending on their frequency of occurrence. Taken together, the results indicate that an N400 priming effect is only evoked when the task performance induces the semantic aspects of words to become part of an episodic trace of the stimulus event.

Adult↗
PubMed2000

Vocal control of acoustic information for sonar discriminations by the echolocating bat, Eptesicus fuscus.

This study aimed to determine whether bats using frequency modulated (FM) echolocation signals adapt the features of their vocalizations to the perceptual demands of a particular sonar task. Quantitative measures were obtained from the vocal signals produced by echolocating bats (Eptesicus fuscus) that were trained to perform in two distinct perceptual tasks, echo delay and Doppler-shift discriminations. In both perceptual tasks, the bats learned to discriminate electronically manipulated playback signals of their own echolocation sounds, which simulated echoes from sonar targets. Both tasks utilized a single-channel electronic target simulator and tested the bat's in a two-alternative forced choice procedure. The results of this study demonstrate changes in the features of the FM bats' sonar sounds with echolocation task demands, lending support to the notion that this animal actively controls the echo information that guides its behavior.

Animals↗
PubMed2004

Face-gender discrimination is possible in the near-absence of attention.

The attentional cost associated with the visual discrimination of the gender of a face was investigated. Participants performed a face-gender discrimination task either alone (single-task) or concurrently (dual-task) with a known attentional demanding task (5-letter T/L discrimination). Overall performance on face-gender discrimination suffered remarkably little under the dual-task condition compared to the single-task condition. Similar results were obtained in experiments that controlled for potential training effects or the use of low-level cues in this discrimination task. Our results provide further evidence against the notion that only low-level representations can be accessed outside the focus of attention.

Adult↗
PubMed1999

Depressed mood in multiple sclerosis: relationship to capacity-demanding memory and attentional functioning.

Because it is theorized that depression results in reduced available attentional capacity that, in turn, can explain the impaired performance on capacity-demanding tasks in depressed individuals, the authors predicted that multiple sclerosis (MS) patients with depressed mood would have difficulty with these types of tasks. Twenty depressed mood MS participants were compared with 41 nondepressed mood MS participants and 8 nondepressed mood controls on 5 attentional capacity-demanding clinical memory and attentional tasks and 3 tasks with minimal capacity demands. Depressed mood MS patients performed significantly worse than both nondepressed mood groups on the 3 speeded capacity-demanding attentional measures but not on any of the tasks requiring few capacity demands, supporting the authors' predictions. The possibility that the impaired performance of depressed mood MS patients on speeded attentional tasks was mediated by reduced verbal working memory capacity, impaired deployment of executive strategies that access working memory capacity, or psychomotor slowing is explored.

Attention↗