An automated bisection device for assessing attentional neglect in clinical populations

An automated bisection device (ABD) is described that is designed for use in assessing the direction of three-dimensional neglect in various clinical populations. This device features an apparatus containing two base sections and a connecting rod, on which is located a bisection indicator assemblage that can be moved either by hand or by a calibrated motor-drive system. The indicator assemblage is, in turn, connected to a motor-control box with variable speed settings and a digital readout. The ABD can be used to measure bisection estimations along all three linear axes (lateral, vertical, and depth) by providing visual cues alone, tactile cues alone, or a combination of visual and tactile cues.     

Electrophysiological and behavioral indicants of selective attention to multifeature gratings

The mechanisms underlying selective attention to gratings consisting of a particular conjunction of spatial frequency and orientation were investigated by means of both visual evoked potential (VEP) and behavioral measures. The effects of selective attention upon the VEP indicated two general types of selection processes: one which is specific to the features contained in the relevant gratings and is most pronounced approximately 225 msec post-stimulation, and another which is specific to the conjunction of features defining the relevant grating and is most pronounced 250–375 msec following the presentation of the stimulus. The behavioral responses primarily reflected this latter, or grating-specific, attentional process. The results are discussed in terms of the role of sensory feature channels in mediating selective attention to visual stimuli and are related to various information processing models of visual pattern selection.     

Target-tilt and vertical-hemifield asymmetries in free-scan search for 3-D targets

In this study, asymmetries in finding pictorial 3-D targets defined by their tilt and rotation in space were investigated by means of a free-scan search task. In Experiment 1, feature search for cube tilt and rotation, as assessed by a spatial forced-choice task, was slow but still exhibited a characteristic “flat” slope; it was also much faster to upward-tilted cubes and to targets located in the upper half of the search field. Faster search times for cubes and rectangular solids in the upper field, an advantage for upward-tilted cubes, and a strong interaction between target tilt and direction of lighting (upward or downward) for the rectangular solids were all demonstrated in Experiment 2. Finally, an advantage in searching for tilted cubes located in the upper half of the display was shown in Experiment 3, which used a present-absent search task. The results of this study confirm that the upper-field bias in visual search is due mainly to a biased search mechanism and not to the features of the target stimulus or to specific ecological factors.     

Binocular interaction of orientation and spatial frequency channels: Evoked potentials and observer sensitivity

The interaction between size and orientation feature processing in the human visual system was investigated. Both observer sensitivity (d’ss) and the visual evoked potential (VEP) to test gratings flashed to one eye were investigated as a function of the nature of a continuously presented suppressing grating viewed either by that same eye or the opposite eye. The test and suppressing gratings were varied both in bar width (9′ss vs. 36′ss) and orientation (vertical vs. horizontal). The continuous grating intra- and interocularly suppressed the monocular VEPs to the flashed grating, the specificity of the suppression depending on the latency at which VEP amplitude was measured. VEP amplitude measured at early latencies (100–125 msec) was suppressed primarily when the flashed and continuous gratings were the same orientation, regardless of size. Starting at about 200 msec, and thereafter, VEP amplitudes were suppressed when the continuous bars were either the same orientationor size as the flashed bars. Late latencies, starting at 220 msec, and thereafter, were suppressed primarily when the bars in the two gratings were the same orientation and size. The reduction in observer sensitivity (d′ss) paralleled the changes found in the late VEP measures. These effects were evident under both the intraocular and interocular suppressing conditions. This pattern of VEP suppression, measured across eight points in the VEP waveform, was interpreted as indicating the existence of a sequence of channels that are specific first to a particular grating orientation, then to either a particular grating spatial frequency or orientation, and finally to the conjunction of a particular orientation and spatial frequency. Both sequential and parallel feature processing appears to take place in the human visual cortex, with grating orientation being encoded earlier than grating size.     

Assessing the Legacy of the GBG Model

A critique of the article by Bryden, McManus, and Bulman-Fleming ("Evaluating the empirical support for the Geschwind-Behan-Galaburda model of cerebral lateralization") is presented. Bryden et al. expose some of the principal weaknesses of the cerebral lateralization model put forth by Geschwind and colleagues and contribute an important meta-analysis of findings concerning the model′s predicted relationship between immune disorders and handedness. Nonetheless, the theory put forth by Geschwind and colleagues retains an important legacy despite a multitude of faulty assumptions and predictive failures. Also offered is a brief synopsis of a new model that explains the many positive relationships found among various neurodevelopmental disorders and medical conditions, as well as why abnormal handedness distributions occur in some but not other neurodevelopmental disorders.     

Dopamine and the origins of human intelligence

A general theory is proposed that attributes the origins of human intelligence to an expansion of dopaminergic systems in human cognition. Dopamine is postulated to be the key neurotransmitter regulating six predominantly left-hemispheric cognitive skills critical to human language and thought: motor planning, working memory, cognitive flexibility, abstract reasoning, temporal analysis/sequencing, and generativity. A dopaminergic expansion during early hominid evolution could have enabled successful chase-hunting in the savannas of sub-Saharan Africa, given the critical role of dopamine in counteracting hyperthermia during endurance activity. In turn, changes in physical activity and diet may have further increased cortical dopamine levels by augmenting tyrosine and its conversion to dopamine in the central nervous system (CNS). By means of the regulatory action of dopamine and other substances, the physiological and dietary changes may have contributed to the vertical elongation of the body, increased brain size, and increased cortical convolutedness that occurred during human evolution. Finally, emphasizing the role of dopamine in human intelligence may offer a new perspective on the advanced cognitive reasoning skills in nonprimate lineages such as cetaceans and avians, whose cortical anatomy differs radically from that of primates.     

Why your "head is in the clouds" during thinking: the relationship between cognition and upper space

Higher-order cognition in humans has not generally been viewed as closely entwined with the brain mechanisms mediating more basic perceptual-motor interactions in 3-D space. However, recent findings suggest that perceptual and oculomotor mechanisms that are biased toward the upper field (which disproportionately represents radially distant space) are activated during complex mental operations, ranging from semantic processing to mental arithmetic and memory search. The particularly close affinity with upward conjugate eye deviations--further confirmed in a study of 24 schoolchildren who responded to various mental questions and demands--suggests that active, abstract thinking in humans may have expropriated the focal-extrapersonal brain systems involved in saccadic exploration of the distant environment in other primates.     

Effects of sleep deprivation on cognitive performance by United States Air Force pilots

This study examined the effects of 35 h of continuous sleep deprivation on performance in a variety of cognitive tasks as well as simulated flight. Ten United States Air Force pilots completed the Multi-Attribute Task Battery (MATB), Psychomotor Vigilance Task (PVT), and Operation Span Task (OSPAN), as well as simulated flight at 3 h intervals over a 35 h sleep deprivation period. Performance declined on all tests after about 18–20 h of continuous sleep deprivation, although the degree to which performance degraded varied. During the second half of the sleep deprivation period, performance on the simulated flight was predicted by PVT and OSPAN reasonably well but much less so by the MATB. Variance from optimal flight performance was predicted by both PVT and OSPAN but each measure added incremental validity to the prediction. The two measures together accounted for 58% of the variance in flight performance in the second half of the sleep deprivation period.     

Target-tilt and vertical-hemifield asymmetries in free-scan search for 3-D targets.

In this study, asymmetries in finding pictorial 3-D targets defined by their tilt and rotation in space were investigated by means of a free-scan search task. In Experiment 1, feature search for cube tilt and rotation, as assessed by a spatial forced-choice task, was slow but still exhibited a characteristic "flat" slope; it was also much faster to upward-tilted cubes and to targets located in the upper half of the search field. Faster search times for cubes and rectangular solids in the upper field, an advantage for upward-tilted cubes, and a strong interaction between target tilt and direction of lighting (upward or downward) for the rectangular solids were all demonstrated in Experiment 2. Finally, an advantage in searching for tilted cubes located in the upper half of the display was shown in Experiment 3, which used a present-absent search task. The results of this study confirm that the upper-field bias in visual search is due mainly to a biased search mechanism and not to the features of the target stimulus or to specific ecological factors.