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PubMed1978

Visual detection of spatial contrast; influence of location in the visual field, target extent and illuminance level.

A model is proposed that permits the prediction of contrast detection thresholds for arbitrary spatial patterns. The influence of the inhomogeneous structure of the visual field and a form of spatial integration are incorporated in the model. A hypothetical density function for the spatial sampling units, which specifies the distribution of these units with respect to both size and location, is described. The density function is compared with anatomical and electrophysiological knowledge of the density of retinal and cortical receptive fields. This density function permits a particularly lucid interpretation in terms of pattern processing. It can be considered as a system that permits simultaneous global and focal views of the surroundings. Thedensity function, together with a schematized adaptation behaviour of single units, and an incoherent summation rule permit us to calculate a measure of the mass response, and consequently the threshold function. Predictions of the model are compared with recently obtained psychophysical data. In particular an explanation is offered for certain invariance properties of spatial contrast detection that seems to possess promising generality.

Animals↗

PubMed1992

Covert orienting to central visual cues and sport practice relations in the development of visual attention.

This study examines the development of controlled covert orienting of visual attention, according to the age and the level of performance of tennis players. Practicers and nonpracticers age 13, 16, and 25 participated in a covert orienting task. On each trial, subjects responded to a target which appeared in one of four locations arrayed horizontally across the display. Three central cues were used: neutral, the cue did not specify in which location the target would appear; valid, the target was present in the cued location on 80% of the trials; invalid, the target was present in one of the uncued locations on the remaining 20% of the trials. The results showed that (1) practicers were not faster than nonpracticers in processing the signals, (2) observers of all ages oriented attention voluntarily to the cued locations, (3) central cues had a smaller effect on older and practiced subjects, and (4) developmental and sport practice factors had similar effects on orienting efficiency. The implications of these findings for theories of attentional development are discussed.

Adolescent↗

PubMed1986

CBF gradient changes elicited by visual stimulation and visual memory tasks.

Normal volunteers underwent three successive scans of regional cerebral blood flow (rCBF) using the 133Xe inhalation technique during visual stimulation, a recognition memory task and a resting state defined by high EEG alpha content. Since the stimulation was virtually identical in both non-rest conditions, we were able to separate the CBF pattern resulting from simple stimulation and that resulting from the cognitive (recognition memory) component alone. These turned out to have very nearly opposite effects on the normal anterior-to-posterior resting state gradient: the sensory component diminished the gradient, while the cognitive component exaggerated it. It is suggested that these normative data can be of clinical value in the study of cerebral recovery/reorganization following post-traumatic amnesia.

Adult↗

PubMed2004

Three-month-olds' visual preference for faces and its underlying visual processing mechanisms.

This study was aimed at investigating the face preference phenomenon and its underlying mechanisms at 3 months of age. Using an eye-tracker apparatus, Experiment 1 demonstrated that 3-month-olds prefer natural face images to unnatural ones, replicating and extending previous evidence obtained with schematic facelike stimuli. Experiments 2 and 3 showed that the general mechanisms that induce face preference in newborns could not explain the same phenomenon at 3 months of age, when infants are attracted by perceptual cues more specific to faces. This suggests that signs of a process of cognitive specialization are already present in 3-month-olds' visual behavior toward faces.

Choice Behavior↗

PubMed2003

Early sensory information processes are enhanced on visual oddball and S1-S2 tasks in Parkinson's disease: a visual event-related potentials study.

To observe sensory and cognitive information processing in Parkinson's disease (PD), 34 PD patients and 26 controls were investigated. A visual oddball paradigm and an S1-S2 paradigm were employed to record the early (P1, N1, P2) and late (N2, P3) event-related potentials (ERPs) at Cz, Pz and Oz. Results showed: (1) enlarged P1 amplitude at all electrode locations on both tasks, (2) shortened N1 latency and enlarged P2 amplitude at Oz on both tasks, (3) enlarged N1 amplitude at Cz during an oddball paradigm, (4) delayed N2 latency and decreased N2, P3 amplitude on both tasks, and (5) delayed P3 latency and reaction time during the S1-S2 paradigm. Abnormal ERP changes were correlated with worsened scores on Wechsler Adult Intelligence Scale-Revised and motor dysfunction scales in PD. We surmise overactive aspects or failed inhibitory modulation of sensory information processing in the early ERP stage and deficient cognitive information processing during the late ERP stage in PD.

Adult↗

PubMedDate not supplied

Fundamentally misunderstanding visual perception. Adults' belief in visual emissions.

The authors reviewed research about a profound misconception that is present among college students, namely, the belief that the process of vision includes emanations from the eyes, an idea that is consistent with the extramission theory of perception, which was originally professed by early Greek philosophers and which persisted in scholarly circles for centuries. The authors document the strength and breadth of this phenomenon and the object failure of traditional educational techniques to overcome this belief, and they reveal that students are leaving psychology courses with a flawed understanding of one of the most studied processes in the history of psychology--visual perception. Some suggestions are offered for overcoming this misconception in traditional college classroom settings.

Adolescent↗

PubMed2002

Visual marking and visual change.

Five experiments investigated the types of changes that disrupt the preview effect--the benefit gained in difficult search tasks from presenting some distractors earlier in time. A shape change with or without an overall luminance change at the location of an old item was found to disrupt the preview effect, whereas an equivalent luminance change alone or an isoluminant color change was not disruptive. Results suggest that (a) relatively low-level visual changes may not be sufficient to abolish the benefit, (b) the benefit most likely occurs through inhibition applied to locations within a location master map, and (c) inhibition need not be applied to surface features of objects.

Adolescent↗

PubMed1983

Is continuous visual monitoring necessary in visually guided locomotion?

Subjects were asked to walk to targets that were up to 21 m away, either with vision excluded during walking or under normal visual control. Over the entire range, subjects were accurate whether or not vision was available as long as no more than approximately 8 sec elapsed between closing the eyes and reaching the target. If more than 8 sec elapsed, (a) this had no influence on distances up to 5 m, but (b) distances between 6-21 m were severely impaired. The results are interpreted to mean that two mechanisms are involved in guidance. Up to 5 m, motor programs of relatively long duration can be formulated and used to control activity. Over greater distances, subjects internalized information about the environment in a more general form, independently of any particular set of motor instructions, and used this to control activity and formulate new motor programs. Experiments in support of this interpretation are presented.

Adult↗

PubMed1981

Orientation selectivity of the human visual system as a function of retinal eccentricity and visual hemifield.

An adaptation method was used to determine the specificity of orientation-selective channels in the human visual system at different retinal eccentricities (up to 16 deg) in both hemifields of each eye. For a vertical test grating, the elevation in contrast threshold produced by adapting to a high-contrast grating of the same spatial frequency but variable orientation was equated with the contrast levels of a vertical adapting grating that produced equivalent effects (equivalent-contrast transformation). This enabled comparisons to be made between the orientation tuning of the aftereffect at different retinal loci. For the spatial frequency employed (3 cycles deg-1), no systematic change in orientation selectivity was found as a function of either retinal eccentricity or the hemifield (and hence the cerebral hemisphere) stimulated.

Adaptation, Ocular↗

PubMed1993

Interaction of visual and tactile information in the control of chicks' locomotion in the visual cliff.

The behaviour of two-day-old chicks placed on the deep side of a visual cliff was examined. With increasing depth of the floor below the chicks, latency to move over the deep side towards another chick on the shallow side increased, while speed of locomotion decreased. Chicks given the same incentive to step over a visible edge onto the deep side showed a stronger inhibition of movement at all depths, indicating that absolute depth of a surface and relative depth of an edge affect behaviour differently. At depths greater than 4 cm, the majority of chicks performed a jump from the deep to the shallow side, and the distances over which they jumped corresponded to those jumped when tested with a real gap. These results suggest that detection of the far side of a gap alone is sufficient to elicit a jump. Just before jumping, chicks adopted a head orientation which depended on the vertical distance of the cliff edge below them. Changes in head orientation did not maintain retinal fixation of the edge, and may instead be important in setting the correct direction of thrust when jumping.

Animals↗

PubMed2003

Visual processing of coherent rotation in the central visual field: an fMRI study.

Functional magnetic resonance imaging was used to determine the brain areas that process coherent motion. To reduce the activity related to eye-movement planning and self-motion perception, rotation was used as coherent motion and the stimulus was restricted to the central visual field. Coherent rotation relative to incoherent random-dot motion resulted in consistent activation in the superior parietal lobule (SPL), in the lateral occipital gyrus (presumptive kinetic occipital region, KO), and in the fusiform gyrus (FG). The main novel finding in present study is the bilateral SPL activation, which has not been found in any previous study contrasting coherent and incoherent motion. It is suggested that the SPL activation is related to form-from-motion processing. The stimulus modification that prevented abrupt appearances of dots at the borders of the stimulus field increased the strength of rolling disk-like percept of the coherent stimulus. This perception of form may also be at least partly responsible for the activation in KO and FG. With this explanation, our three consistent activation areas are in line with previous findings. Furthermore, these results demonstrate that even delicate changes in some stimulus aspects can lead to significant changes in the activation of the brain.

Adult↗

PubMed2005

Dissociation between visual perception of allocentric distance and visually directed walking of its extent.

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.

Adult↗

PubMed2003

Motility of dendritic spines in visual cortex in vivo: changes during the critical period and effects of visual deprivation.

Cortical dendritic spines are highly motile postsynaptic structures onto which most excitatory synapses are formed. It has been postulated that spine dynamics might reflect synaptic plasticity of cortical neurons. To test this hypothesis, we have investigated spine dynamics during the critical period in mouse visual cortex in vivo with and without sensory deprivation. The motility of spines on apical dendrites of layer 5 neurons was assayed by time-lapse two-photon microscopy. Spines were motile at the ages examined, postnatal days (P)21-P42, although motility decreased between P21 and P28 and then remained stable through P42. Binocular deprivation from before the time of eye-opening up-regulated spine motility during the peak of the critical period (P28), without affecting average spine length, class distribution, or density. Deprivation at the start of the critical period had no effect on spine motility, whereas continued deprivation through the end of the critical period appeared to reduce spine motility slightly. We conclude that spine motility might be involved in critical-period plasticity and that reduction of activity during the critical period enhances spine dynamics.

Aging↗

PubMedDate not supplied

Monkey perirhinal cortex is critical for visual memory, but not for visual perception: reexamination of the behavioural evidence from monkeys.

Overdependence on discrimination learning paradigms to assess the function of perirhinal cortex has complicated understanding of the cognitive role of this structure. Impairments in discrimination learning can result from at least two distinct causes: (a) failure to accurately apprehend and represent the relevant stimuli, or (b) failure to form and remember associations between stimulus representations and reward. Thus, the results of discrimination learning experiments do not readily differentiate deficits in perception from deficits in learning and memory. Here I describe studies that do dissociate learning and memory from perception and show that perirhinal cortex damage impairs learning and/or memory, but not perception. Reanalysis and reconsideration of other published data call into further question the hypothesis that the monkey perirhinal cortex plays a critical role in visual perception.

Animals↗

PubMed1984

Visual motor co-ordination and dynamic visual acuity.

Data on the effect of an antihistamine (triprolidine 10 mg) on visuo-motor coordination and dynamic visual acuity were used to establish interactions between these skills. Analysis of covariance and principal component analysis were used. The analyses suggested two main effects--an effect on the activity of the neuromuscular system and one which impaired ability to anticipate target movement. Detection of impaired performance by any task may have wider implications to the effectiveness of the individual than that obviously suggested by the skill itself.

Humans↗

PubMed1971

Visual attention in the tree shrew: an ablation study of the striate and extrastriate visual cortex.

Removal of the striate area in tree shrews results in increased distractibility, which prevents the animals from learning to discriminate form when hue is an irrelevant and distracting cue. Removal of the extrastriate visual cortex results in the reciprocal deficit: an increase in perseveration manifested by an inability to shift attention when irrelevant dimensions are made relevant.

Animals↗

PubMed1982

Blink reflexes elicited by electrical, acoustic and visual stimuli. II. Their relation to visual-evoked potentials and auditory brain stem evoked potentials in the diagnosis of multiple sclerosis.

Blink reflexes, elicited by flashes of light, tone bursts and electrical stimuli, as well as checkerboard reversal visual-evoked potentials and brain stem auditory evoked potentials were investigated in 55 patients with different degrees of diagnostic probability of multiple sclerosis. It is demonstrated that electrically and acoustically elicited blink reflexes are simple but rather sensitive methods of indicating brain stem lesions. They should be used complementarily with brain stem auditory potentials. Flash-elicited blink reflexes, although sensitive, are thought to be of minor importance, since they give only restricted localizing information.

Acoustic Stimulation↗

PubMed2004

Partitioning visual displays aids task-directed visual search.

We reduced time to detect target symbols in mock radar screens by adding perceptual boundaries that partitioned displays in accordance with task instructions. Targets appeared among distractor symbols either close to or far from the display center, and participants were instructed to find the target closest to the center. Search time increased with both number of distractors and distance of target from center. However, when close and far regions were delineated by a centrally presented "range ring," the distractor effect was substantially reduced. In addition, eye movement patterns more closely resembled a task-efficient spiral when displays contained a range ring. Results suggest that the addition of perceptual boundaries to visual displays can help to guide search in accordance with task-directed constraints. Actual or potential applications of this research include the incorporation of perceptual boundaries into display designs in order to encourage task-efficient scanpaths (as identified via task analysis and/or empirical testing).

Adult↗