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PubMed2003

Functional MRI studies of human visual motion perception: texture, luminance, attention and after-effects.

Motion of an object is thought to be perceived independently of the object's surface properties. However, theoretical, neuropsychological and psychophysical observations have suggested that motion of textures, called 'second-order motion', may be processed by a separate system from luminance-based, or 'first-order', motion. Functional magnetic resonance imaging (fMRI) responses during passive viewing, attentional modulation and post-adaptation motion after-effects (MAE) of these stimuli were measured in seven retinotopic visual areas (labeled V1, V2, V3, VP, V4v, V3A and LO) and the motion-sensitive area MT/MST (V5). In all visual areas, responses were strikingly similar to motion of first- and second-order stimuli. These results differ from a prior investigation, because here the motion-specific responses were isolated. Directing attention towards and away from the motion elicited equivalent response modulation for the two types. Dramatic post-adaptation (MAE) differences in perception of the two stimuli were observed and fMRI activation mimicked perceptual changes, but did not reveal the processing differences. In fact, no visual area was found to respond selectively to the motion of second-order stimuli, suggesting that motion perception arises from a unified motion detection system.

Adolescent↗

PubMed2001

Mechanisms of migraine aura revealed by functional MRI in human visual cortex.

Cortical spreading depression (CSD) has been suggested to underlie migraine visual aura. However, it has been challenging to test this hypothesis in human cerebral cortex. Using high-field functional MRI with near-continuous recording during visual aura in three subjects, we observed blood oxygenation level-dependent (BOLD) signal changes that demonstrated at least eight characteristics of CSD, time-locked to percept/onset of the aura. Initially, a focal increase in BOLD signal (possibly reflecting vasodilation), developed within extrastriate cortex (area V3A). This BOLD change progressed contiguously and slowly (3.5 +/- 1.1 mm/min) over occipital cortex, congruent with the retinotopy of the visual percept. Following the same retinotopic progression, the BOLD signal then diminished (possibly reflecting vasoconstriction after the initial vasodilation), as did the BOLD response to visual activation. During periods with no visual stimulation, but while the subject was experiencing scintillations, BOLD signal followed the retinotopic progression of the visual percept. These data strongly suggest that an electrophysiological event such as CSD generates the aura in human visual cortex.

Adult↗

PubMed2006

Perception of visual motion coherence by rats and mice.

The coherence thresholds to discriminate the direction of motion in random-dot kinematograms were measured in rats and mice. Performance was best in the rats when dot displacement from frame-to-frame was about 2 degrees, and frame duration was less than 100 ms. Mice had coherence thresholds similar to those of rats when tested at the same step size and frame duration. Although the lowest thresholds in the rats and mice occasionally reached human levels, average rodent values ( approximately 25%) were 2-3 times higher than those of humans. These data indicate that the rodent and primate visual systems are similar in that both have local motion detectors and a system for extracting global motion from a noisy signal.

Animals↗

PubMed1992

Cortical dynamics of visual motion perception: short-range and long-range apparent motion.

This article describes further evidence for a new neural network theory of biological motion perception. The theory clarifies why parallel streams V1----V2, V1----MT, and V1----V2----MT exist for static form and motion form processing among the areas V1, V2, and MT of visual cortex. The theory suggests that the static form system (Static BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast and to direction-of-motion, whereas the motion form system (Motion BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast but sensitive to direction-of-motion. The theory is used to explain classical and recent data about short-range and long-range apparent motion percepts that have not yet been explained by alternative models. These data include beta motion, split motion, gamma motion and reverse-contrast gamma motion, delta motion, and visual inertia. Also included are the transition from group motion to element motion in response to a Ternus display as the interstimulus interval (ISI) decreases; group motion in response to a reverse-contrast Ternus display even at short ISIs; speed-up of motion velocity as interflash distance increases or flash duration decreases; dependence of the transition from element motion to group motion on stimulus duration and size, various classical dependencies between flash duration, spatial separation, ISI, and motion threshold known as Korte's laws; dependence of motion strength on stimulus orientation and spatial frequency; short-range and long-range form-color interactions; and binocular interactions of flashes to different eyes.

Attention↗

PubMed1994

Neurobehavioral characteristics of CGG amplification status in fragile X females.

Neurobehavioral correlates of CGG amplification were studied in 17 nonretarded adult female carriers of fragile X syndrome. The results revealed a significant relationship between IQ and the number of CGG repeats in the 5' untranslated region of the FMR1 gene. Women with a full mutation (> 200 CGG repeats) scored below average in IQ, visual-spatial perception, visual-spatial organization, and executive function. There were no differences in fine motor dexterity or memory as a function of CGG amplification status. A history of major depressive disorder was identified in 71% of the sample, but incidence of depression was not associated with the degree of CGG amplification. Schizotypal features were noted in 18%. No intellectual or neuropsychological deficit was found in women with a premutation (< 200 CGG repeats). Decrements in IQ, visual-spatial perception, and executive function appear to arise as a consequence of the CGG amplification.

Adult↗

PubMed1990

Close binding of identity and location in visual feature perception.

The binding of identity and location information in disjunctive feature search was studied. Ss searched a heterogeneous display for a color or a form target, and reported both target identity and location. To avoid better than chance guessing of target identity (by choosing the target less likely to have been seen), the difficulty of the two targets was equalized adaptively; a mathematical model was used to quantify residual effects. A spatial layout was used that minimized postperceptual errors in reporting location. Results showed strong binding of identity and location perception. After correction for guessing, no perception of identity without location was found. A weak trend was found for accurate perception of target location without identity. We propose that activated features generate attention-calling "interrupt" signals, specifying only location; attention then retrieves the properties at that location.

Adult↗

PubMed1999

A prospective study of cognitive impairment in ALS.

OBJECTIVE: To characterize prospectively the cognitive profile in ALS. METHODS: Clinically definite ALS patients (11 men, 2 women), age 39.9 to 74.0 years (mean age, 54.2 +/- 9.6 years; mean disease duration, 21.1 +/- 10.5 months) underwent neuropsychologic, language, and speech testing followed by MR 1H spectroscopy (4 T). Five spousal control subjects completed an identical protocol. Eight ALS patients participated in follow-up studies at a 6-month interval. RESULTS: Relative to control subjects, ALS patients showed mild impairment in word generation, recognition memory (faces), and motor-free visual perception. Bulbar-onset patients showed greater impairment in a number of measures (working memory, problem solving/cognitive flexibility, visual perception, and recognition memory for words and faces), and cognitive impairment appeared more progressive over time. ALS patients demonstrated anomia on a confrontation naming test, with no significant problems following commands or repeating. Speech motor performance scores and intelligibility scores were not significantly different. No significant declines in forced vital capacity, forced expiratory volume, or peak expiratory flow rates were observed. Although normal at initial testing (T1), MR 1H spectroscopy demonstrated a reduction of the N-acetylaspartate/creatine (NAA/Cr) ratio in the nondominant precentral motor strip across the two testing intervals. In contrast, the NAA/Cr ratio obtained from the anterior cingulate gyrus at T1 was already reduced in bulbar-onset patients (p < 0.001), whereas no deficits were observed in limb-onset individuals in the same region. CONCLUSIONS: Bulbar-onset ALS patients with cognitive impairments and neuronal loss in the anterior cingulate gyrus subsequently developed more profound neuropsychological dysfunction whereas both language and speech capabilities remained relatively preserved. Of note, the absence of bulbar signs did not predict an absence of cognitive decline.

Adult↗

PubMed2006

The perception of animacy in young children with autism.

Visual perception may be a developmental prerequisite to some types of social understanding. The ability to perceive social information given visual motion appears to develop early. However, children with autism have profound deficits in social cognitive function and may fail to see social motion in the same way that typically developing children do. We tested the hypothesis that children with autism fail to discriminate animate motion, using a novel paradigm involving simple geometric figures. The subjects were 23 children with autism (c.a. 70.7 mos.), 18 children with other developmental disabilities (c.a. 68.2 mos.), and 18 typically developing children (c.a. 46.4 mos.). Children saw two circles moving on a screen and were rewarded for identifying the one that moved as if animate. A control condition required children to identify the heavier of two objects. Children with autism initially showed a deficit in categorizing objects as animate (though no deficit on the control task), but showed no deficit in this ability after they had reached criterion in the training phase. These results are discussed in terms of the social orienting theory of autism, and the possibility that animacy perception might be preserved in autism, even if it is not used automatically.

Autistic Disorder↗

PubMed1996

Inattention and the perception of visual feature conjunctions.

Visual processing of objects in the absence of focused attention appears to be limited. We varied the degree of attention, or visual processing, that observers paid to objects using an instruction set manipulation. In 2 experiments, subjects performed tasks that required superficial or detailed visual analysis of the objects involved. In subsequent recognition tests, information about conjunctions of shape and internal color/texture pattern was limited when only superficial visual analysis was required to encode the object. This implies that the degree of visual processing, during object encoding affects the likelihood that feature conjunctions are incorporated into the visual representation of these objects.

Adult↗

PubMed1993

Nonlinear combination rules and the perception of visual motion transparency.

Experiments were performed to elucidate the decomposition performed by the human visual system in the segregation of complex motion stimuli into distinct moving surfaces. Subjects were presented with achromatic patterns consisting of four types of elements, generated from two random binary luminance patterns (random-dot checkerboards). The luminance of each of the four region classes was under program control. Animated sequences of such images were produced by displacing each of the two generating patterns in opposite directions on a frame by frame basis. These displays evoke a wide variety of percepts, depending on the programmed luminance values, including motion in a single direction, simultaneous motions of transparent sheets in opposite directions, dynamic noise with no directional component, or any combination of the above percepts. A theory is presented which relates the strengths of these percepts to the amplitudes of the components in the perceptual decomposition. The experiments described measured thresholds for seeing noise or "twinkling" in addition to the multiple motions, with the goal of determining the particular signal transformations preceding motion analysis. The results are consistent with a motion extraction mechanism which operates on a linear representation of the input imagery. These results extend a similar finding due to Anstis and Mather [(1985) Perception, 14, 167-179] and call into question the interpretation of a recent study by Stoner, Allbright and Ramachandran [(1990) Nature (London), 344, 153-155].

Contrast Sensitivity↗

PubMed1963

Disappearance of luminous designs.

When a subject fixates on a luminous design under conditions of low illumination, he experiences a fragmenting disappearance of the figure. This fragmentation occurs in meaningful units and is comparable to the disappearance of images stabilized on the retina. The luminous paint technique offers a new and simple approach to the study of visual perception.

Humans↗

PubMedDate not supplied

Distortions in two-dimensional visual space perception in strabismic observers.

Amblyopic subjects were asked to memorize circles of different radii (2, 4 and 6 degrees), and then to reconstruct them monocularly with each eye, point by point (12 points per circle). The resulting two-dimensional maps of visual space showed considerable distortions, including expansion, shrinkage and torsion of specific regions of the visual field of the amblyopic eye, but not the normal eye. Based on the differences between the two eyes, we computed complex two-dimensional patterns (gratings, checkerboards, optotypes, written text, natural scenes) as "seen" monocularly with the amblyopic eye. These reconstructed patterns were then compared with drawings of the same patterns observed through the amblyopic eyes of the same subjects. The reconstructed patterns only partially reflected the actual perception for the amblyopic eyes. The compensation of complex, globally-extended scenes in comparison to the distortions obtained by local, punctate settings probably reflects cooperative interactions occurring at higher brain levels.

Adult↗

PubMed2001

Effects of manipulating relative and absolute motion information during observational learning of an aiming task.

In the visual perception perspective of observational learning, the manipulation of relative and absolute motion information in visual demonstrations optimally directs learners' search towards appropriate task solutions. We assessed the effect of emphasizing transformational information and removal of structural information using point-light kinematic displays in approximating the model's relative motion patterns. Participants viewed computer-simulated point-light demonstrations or normal video demonstrations before and intermittently throughout 100 acquisition trials with knowledge of results on an underarm modified-dart aiming task. On the next day, all participants performed 20 retention trials without demonstrations. The kinematics of spatial and temporal coordination and control variables were examined relative to the model's action, as well as performance scores. The results indicated that approximation of the model's spatial and temporal coordination and control patterns was achieved after observation of either type of demonstrations. No differences were found in movement outcomes. In a second experiment, the effects of manipulating absolute motion information by slow-motion demonstrations were examined relative to real-time demonstrations. Real-time demonstrations led to a closer approximation to the model's spatial and temporal coordination patterns and better outcome scores, contradicting predictions that slow-motion displays convey intact relative motion information. We speculate that the effect of visual demonstration speed on action perception and reproduction is a function of task constraints--that is, novelty or familiarity of relative motion of demonstrated activities.

Adult↗

PubMed1997

Knowledge in perception and illusion.

Following Hermann von Helmholtz, who described visual perceptions as unconscious inferences from sensory data and knowledge derived from the past, perceptions are regarded as similar to predictive hypotheses of science, but are psychologically projected into external space and accepted as our most immediate reality. There are increasing discrepancies between perceptions and conceptions with science's advances, which makes it hard to define 'illusion'. Visual illusions can provide evidence of object knowledge and working rules for vision, but only when the phenomena are explained and classified. A tentative classification is presented, in terms of appearances and kinds of causes. The large contribution of knowledge from the past for vision raises the issue: how do we recognize the present, without confusion from the past. This danger is generally avoided as the present is signalled by real-time sensory inputs-perhaps flagged by qualia of consciousness.

Cognition↗

PubMed1975

Visual form perception in deficient and normal readers as a function of age and orthographic-linguistic familiarity.

The present investigation directly assessed the hypothesis that poor readers sustain no basic disorder in visual-spatial functioning. In order to extend pervious results to younger children, the performance of poor and normal readers from both the second and sixth grades was compared. Adopting the format of an earlier investigation, a visual recall task was employed as the dependent variable, and it was predicted that poor readers would perform as well as normals with stimuli taken from Hebrew, an unfamiliar orthography. Accordingly, non-Hebrew poor and normal readers were compared with normal readers learning Hebrew on the production of varying length Hebrew words. As anticipated, children in the non Hebrew reader groups performed comparably on this task, but the performance of these subjects was inferior to that of children in the Hebrew groups. The data support the contention that visual perceptual disorder is an unlikely source of reading disability.

Age Factors↗

PubMed2004

Examining the crossmodal consequences of viewing the Müller-Lyer illusion.

For many years, the Müller-Lyer illusion was studied as a purely "visual" illusion, but like many other optical illusions, the evidence now shows that it also occurs when stimuli are presented tactually. In the present study, we investigated whether the visual perception of the illusion would have any crossmodal consequences for haptic perception. The wings-in and wings-out parts of the Müller-Lyer illusion were placed end-to-end, sharing a central fin. This Brentano version of the illusion was presented visually on a screen in front of the participants, who had to compare the "felt" length of two sticks placed on the back of the screen, one behind either part of the illusion. Our results show that the presentation of the visual illusion modified the felt lengths of the sticks presented directly behind the illusion. In particular, the stick presented on the side of space perceived visually as being shorter (behind the wings-in part of the display) was perceived as longer, and vice versa for the stick mounted behind the space perceived visually as longer (behind the wings-out part of the display). These results highlight the crossmodal consequences of the visual perception of the Müller-Lyer illusion for the haptic perception of line length.

Adolescent↗

PubMed1997

[Adaptation of the central nervous system to optical correction].

Wearing spectacles imply an adjustment of the visual perception and eye movements. The visual cortex accounts for this plasticity, including at the adulthood, especially by the shift or the sprading of the receptor fields and the adjustment of the sensitivity of the primary visual cortex cells to spatial orientation and movement. The cerebellum modulates the vestibulo-ocular reflex gain. The adjustment latencies range from a few minutes to several days according to the disturbancy severity, the drug interferences and the age and medical history of the subject. Neurotrophins seem to be essential for this adjustment and might become an efficient tool to extend the plasticity period.

Adaptation, Physiological↗

PubMed2005

Visual dysfunction in Parkinson disease without dementia.

OBJECTIVE: To determine the profiles of visual dysfunction and their relationship to motor and cognitive dysfunction and to disability in mild to moderate Parkinson disease (PD) without dementia. METHODS: Seventy-six independently living participants with mild to moderate PD and 161 neurologically normal older adults were studied using a comprehensive battery to assess visual acuity, contrast sensitivity (CS), visual speed of processing and attention, spatial and motion perception, visual and verbal memory, visuoconstructional abilities, executive functions, depression, and motor function. RESULTS: Participants with PD scored significantly worse on all tests of vision and cognition compared with normal elderly persons. Reduced CS contributed to deficits on tests of spatial and motion perception and attention in participants with PD. Impairments in visual attention and spatial perception predicted worse cognitive function. Worse performances on tests of visual speed of processing and attention, spatial and motion perception, visual construction, and executive functions correlated with measures of postural instability and gait difficulty (in the Motor section of the Unified Parkinson's Disease Rating Scale). Impairments in motor function, visual memory, mood, and executive functions predicted worse disability as measured by Schwab-England Activities of Daily Living Scale. CONCLUSIONS: Patients with mild to moderate Parkinson disease showed impaired visual perception and cognition compared with elderly control subjects. Visual dysfunction contributes to parkinsonian disability through its influences on cognition and locomotion.

Aged↗