M. Russell Harter

Effects of attention and arousal on visually evoked cortical potentials and reaction time in man

Abstract The combined effects of general arousal and specific attention on averaged evoked potentials and reaction time were studied. Arousal level was manipulated by the presence or absence of a shock threat when the flashes were being presented. Attention was varied by having S react to flashes appearing in either his right or left visual field while ignoring flashes appearing concomitantly but not simultaneously in the opposite field. Potentials evoked under “high” arousal (threat of shock) were greater than those obtained under “low” arousal. Also, reaction times were shorter. The potentials evoked by flashes receiving attention were much greater than those evoked by flashes being ignored. The results indicate that cortical evoked potentials are related to both general arousal and specific attention. The combined effects of increasing or decreasing arousal and shifts in attention toward or away from the evoking stimulus determine whether the net change in evoked potential amplitude will be positive or negative.

Neural processes involved in directing attention

Neural processes associated with two aspects of visual-spatial attention were investigated with event-related potential (ERPs): those that direct spatial attention to a given point in space and those that modulate the processing of sensory input after attention has been directed. The subjects were 6- to 9-year-old children (51 boys and 35 girls). An arrow cue directed attention from the central to peripheral visual field; targets were then flashed in the attended or ignored visual field 600 msec after the cue. The directing of attention to the left vs. right visual field was associated with hemispheric differences in slow potentials prior to the presentation of the targets. The earliest potential, which started about 200 msec after the cue and was negative over the hemisphere contralateral to the direction of attention, was greatest over the parietal area and appeared to reflect processes directing attention per se. The last potential, which peaked 60 msec after the target and was positive over the hemisphere contralateral to the direction of attention, was greatest over the occipital-parietal region. It appeared to reflect the modulation of cortical excitability in the regions receiving input from the relevant and irrelevant visual fields. The effects of spatial attention on P1, N1, and P3 ERP components following the targets replicated previous results. Boys appeared more aroused (as indicated by CNVs) and reflected faster and greater selective processing (as indicated by reaction time, and N1-P1 latency and amplitude) than girls.

Hemispheric differences in the neural processing of stimulus location and type: effects of selective attention on visual evoked potentials.

Hemispheric differences in a negative brain potential associated with selectively attending the location and type of stimulation were investigated. The earlier portion of this negativity (between 125 and 222 msec after stimulation) was associated with attending the location of the stimulus. It was symmetrical in the central scalp regions but was greater in the hemisphere contralateral to the attended visual field in the posterior scalp region. The latter portion of this negativity (from 222 to 272 msec after stimulation) primarily was associated wih attending one of the different types of stimuli presented at a given location and was greater over the left posterior regions of the scalp. These results were interpreted in relationship to the time-course of different types of information processing in the left and right hemisphere.

Evoked cortical responses to checkerboard patterns: Effect of check-size as a function of visual acuity

Abstract The size of checks (5–120′ subtense) comprising checkerboard patterns and the degree of focus (0 to ±5 diopters induced refractive error) of the patterns influenced certain components of visually evoked cortical responses. The amplitude of these components varied non-monotonically with check-size. The check-size which elicited responses of greatest amplitude depended on the magnitude of induced refractive error (degree of defocusing) and thus on visual acuity. When the patterns were sharply focused (no induced refractive error), relatively small checks (10–20′ subtense) elicited responses of greatest amplitude. When the patterns were progressively defocused (±1 to ±5 diopters induced refrractive error), progressively larger checks elicited the greatest responses. The amplitude of VERs appered to be related to the smallest check-size which was clearly percieved.

Attention to pattern orientation: Negative cortical potentials, reaction time, and the selection process ☆

Abstract Six subjects were instructed to give an RT response to one of 3 stimuli randomly presented at a rate of 1/720–1180 msec. The stimuli were diffuse light flashes and grating light flashes with 9′ black and white bars oriented either horizontally or vertically. Attention was controlled by having the subject give an RT response within 375 msec following the relevant stimulus. Evoked potentials to the relevant and irrelevant stimuli were recorded monopolarly over the occipital (O z ), central (C z ), and frontal (F z ) areas of the cortex. Occipital potentials following relevant, as compared to irrelevant, flashes were relatively more negative between 150 and 250 msec poststimulus (O z :N235 potential). The early portion of the negative potential (150–200 msec) reflected selection between diffuse and patterned flashes but not between the orientations of the pattern in the flashes. The later portion of the negative potential (200–250 msec) reflected selection between the orientations of the pattern in the flashes. These results support the hypothesis that occipital potentials following relevant and irrelevant stimuli reflect not only differential processing of relevant and irrelevant information but also reflect a progressive change in the unit or specificity of the differential processing — early and late portions of the negative potential reflecting differential processing on the basis of first the general and then the specific characteristics of the relevant stimulus respectively. In contrast, frontal cortical potentials following relevant stimuli were slightly positive between 150 and 250 msec poststimulus (F z :P235 potential). The unique scalp distribution of these early attention effects suggests that O z :N235 reflects an intramodality underlying process localized in extrastriate visual cortex. A late positive potential peaking at about 370 msec following relevant stimuli (P370) was evident at all electrodes, although it had a central-occipital maximum. Since this potential followed the RT responses, it appeared to reflect processes other than those directly involved in the selective response to relevant stimuli.

Separate verbal memory and naming deficits in attention deficit disorder and reading disability

In this study, verbal memory and naming abilities were investigated in reading disabled (RD) and control children who were characterized according to the presence or absence of attention deficit disorder (ADD). Results indicate that deficits in learning and memory for recently acquired information occur as a function of ADD rather than RD while deficits in naming are specific to RD rather than ADD. We conclude that ADD is a major source of additional and separate cognitive morbidity in RD children.

Effects of contour sharpness and check-size on visually evoked cortical potentials

Abstract Averaged evoked cortical potentials were obtained from S s as they viewed three checkerboard stimulus patterns (checks subtended 12, 20 and 46 min visual angle) through a series of ophthalmic lenses (+6D to −6D). The checkerboards appeared to vary in sharpness of focus under these conditions. Two components of the evoked cortical potential are very sensitive to the sharpness of focus and to the size of the checks in the visual display, a negative one with a latency of 90–100 msec and a positive one with a latency of 180–200 msec. The amplitude of both components decreased as diopter settings were increased and the visual patterns became degraded. The late component was particularly sensitive to check-size under normal viewing conditions. The results suggest that it is possible to determine refractive error by observing the changes in these two components when a stimulus pattern is viewed through a series of lenses.

Cognition and Event‐Related Potentials

Department of Neuroscience Albert Einstein College of Medicine Bronx, New York 10461 Department of Psychiatry Veterans Administration Hospital Palo Alto, California 94305 ‘Institute for Perception Soesterberg, the Netherlands dDepartment of Psychology University of North Carolina Greensboro, North Carolina 2741 2 Department of Neurosciences University of California San Diego, California 92093 /Department of Psychology University of Helsinki 00170 Helsinki 17. Finland gDepartment of Neurology University of California Irvine, California 92668 Hospital de la Salpetriere F-75634 Paris, Cedex 13, France ‘ Nebraska Psychiatric Institute Omaha, Nebraska 68106 RISTO NAATANEN! JOHN POLICH: BERNARD

Evoked cortical responses to checkerboard patterns: effect of check-size as a function of retinal eccentricity.

Visually evoked cortical responses were obtained from 3 Ss as they viewed checkerboard patterned light flashes (checks subtended from 0–180′ of arc) presented to different areas of the retina in respect to the fovea (0–27.5° eccentricity). An inverted “U” —shaped function was obtained between response amplitude and check-size. The check-size which elicited the greatest amplitude responses depended on eccentricity of retinal stimulation: when the foveal area was stimulated, relatively small checks (subtending 15–30′ of arc) evoked the greatest amplitude responses; when progressively more peripheral areas of the retina were stimulated (up to 7.5° eccentricity), progressively larger check-sizes evoked the greatest amplitude responses (subtending up to 60′ of arc). Check-size had little effect on evoked responses when the retina was stimulated 12.5–27.5° from the fovea. The results were discussed in relationship to the assumed size of retinal receptive field centers at different eccentricities in animals and humans.

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.