Visual attention: The past 25 years

Functional specialization in the lower and upper visual fields in humans is analyzed in relation to the origins of the primate visual system. Processing differences between the vertical hemifields are related to the distinction between near (peripersonal) and far (extrapersonal) space, which are biased toward the lower and upper visual fields, respectively. Nonlinear/global processing is required in the lower visual field in order to pergeive the optically degraded and diplopic images in near vision, whereas objects in far vision are searched for and recognized primarily using linear/local perceptual mechanisms. The functional differences between near and far visual space are correlated with their disproportionate representations in the dorsal and ventral divisions of visual association cortex, respectively, and in the magnocellular and parvocellular pathways that project to them. Advances in far visual capabilities and forelimb manipulatory skills may have led to a significant enhancement of these functional specializations.

Functional Specialization in the Lower and Upper Visual Fields in Humans: Its Ecological Origins and Neurophysiological Implications

The spatial and temporal organization of hand and eye movements were studied in normal human subjects as they pointed toward small visual targets. The experiment was designed to assess the role of information about target position in correcting the trajectory of the hand when view of the hand was not available. To accomplish this, the duration of target presentation was systematically varied across blocks of trials. The results of this experiment showed that pointing movements were about 3 times more accurate when the target was present throughout the entire pointing movement, than when the target disappeared shortly after the hand movement had begun. These data indicate that pointing movements made without view of the limb are not purely preprogrammed but instead, are corrected during their execution. These modifications to the motor program are smoothly integrated into the ongoing movement and must depend upon comparing visual information about the position of the target with non-visual information about the position of the limb. The source of this non-visual information was not directly established in the present experiment but presumably must be derived from kinesthetic reafferences and/or efference copy.

Visual control of reaching movements without vision of the limb

Two visual search experiments were carried out using as stimuli large letters made of small identical letters presented in right, or left, or central visual fields. Considering the spatial frequency contents of the stimuli as the critical variable, Experiment 1 showed that a left-field superiority could be obtained whenever a decision had to be made on a large (low frequency) letter alone, and a right-field advantage emerged when a small (high frequency) letter had to be processed. Experiment 2 showed that the two levels of structure of the stimulus were not encoded at the same rate and that at very brief exposure, only the large letter could be accurately identified. This was accompanied by a left-field superiority, whether or not the stimulus contained the target. These results are interpreted as revealing a differential sensitivity of the hemispheres to the spatial frequency contents of a visual image, the right hemisphere being more adept at processing early-available low frequencies and the left hemisphere operating more efficiently on later-available low frequencies. From these and other experiments reviewed, it is suggested that (a) cerebral lateralization of cognitive functions results from differences in sensorimotor resolution capacities of the hemispheres; (b) both hemispheres can process verbal and visuospatial information, analytically and holistically; (c) respective hemispheric competence is a function of the level of sensorimotor resolution required for processing the information available. Language: en

The cerebral balance of power: confrontation or cooperation?

Covert attention affects the psychometric function of contrast sensitivity.

https://pure.tue.nl/ws/files/4238121/734568.pdf

Contrast sensitivity as a function of position on the retina.

https://pure.tue.nl/ws/files/4330141/734567.pdf

Peripheral contrast sensitivity for sine-wave gratings and single periods

Flicker tresholds have been measured with intermittent stimuli as a function of the presentation time of the stimulus. The periods of flickering light were separated by 1-s dark intervals. Under these conditions the flicker threshold depends on the stimulus duration and on the number of cycles in the stimulus. The "De Lange" curves measured in this way can be described by a first-order high-pass filter in combination with a fourth-order low-pass filter.

Flicker sensitivity measured with intermittent stimuli: I. Influence of the stimulus duration on the flicker threshold

The threshold gradient for perception of a linear change in luminance with time has been measured as a function of the stimulus duration. These data are compared with the “De Lange” curves representing the flicker sensitivity measured with intermittent presentation of the stimulus as a function of the stimulus duration. For this purpose it is necessary to take into account the fact that a linear luminance gradient, being a relatively low-frequency signal, is affected less by the low-pass filter supposedly situated in the visual system than by a sinusoidal signal (flicker) of the same duration.

Flicker sensitivity measured with intermittent stimuli: II. Comparison between temporal gradient detection and the "De Lange" curves.

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Contrast sensitivity as a function of position on the retina.

Peripheral contrast sensitivity for sine-wave gratings and single periods

Flicker sensitivity measured with intermittent stimuli: I. Influence of the stimulus duration on the flicker threshold

Flicker sensitivity measured with intermittent stimuli: II. Comparison between temporal gradient detection and the "De Lange" curves.