Recognizing People From Their Movement.

Human observers demonstrate impressive visual sensitivity to human movement. What defines this sensitivity? If motor experience influences the visual analysis of action, then observers should be most sensitive to their own movements. If view-dependent visual experience determines visual sensitivity to human movement, then observers should be most sensitive to the movements of their friends. To test these predictions, participants viewed sagittal displays of point-light depictions of themselves, their friends, and strangers performing various actions. In actor identification and discrimination tasks, sensitivity to one's own motion was highest. Visual sensitivity to friends', but not strangers', actions was above chance. Performance was action dependent. Control studies yielded chance performance with inverted and static displays, suggesting that form and low-motion cues did not define performance. These results suggest that both motor and visual experience define visual sensitivity to human action. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Walking Perception by Walking Observers.

People frequently analyze the actions of other people for the purpose of action coordination. To understand whether such self-relative action perception differs from other-relative action perception, the authors had observers either compare their own walking speed with that of a point-light walker or compare the walking speeds of 2 point-light walkers. In Experiment 1, observers walked, bicycled, or stood while performing a gait-speed discrimination task. Walking observers demonstrated the poorest sensitivity to walking speed, suggesting that perception and performance of the same action alters visual-motion processes. Experiments 2-6 demonstrated that the processes used during self-relative and other-relative action perception differ significantly in their dependence on observers' previous motor experience, current motor effort, and potential for action coordination. These results suggest that the visual analysis of human motion during traditional laboratory studies can differ substantially from the visual analysis of human movement under more realistic conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Viewpoint and the recognition of people from their movements.

Observers can recognize other people from their movements. What is interesting is that observers are best able to recognize their own movements. Enhanced visual sensitivity to self-generated movement may reflect the contribution of motor planning processes to the visual analysis of human action. An alternative view is that enhanced visual sensitivity to self-motion results from extensive experience seeing one's own limbs move. To investigate this alternative explanation, participants viewed point-light actors from first-person egocentric and third-person allocentric viewpoints. Although observers routinely see their own actions from the first-person view, participants were unable to identify egocentric views of their own actions. Conversely, with little real-world experience seeing themselves from third-person views, participants readily identified their own actions from allocentric views. When viewing allocentric displays, participants accurately identified both front and rear views of their own actions. Because people have little experience observing themselves from behind or from third-person views, these findings suggest that visual learning cannot account for enhanced visual sensitivity to self-generated action. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychometrically matched visual-processing tasks in schizophrenia spectrum disorders.

Patients with schizophrenia show deficits in visual perception and working memory, but the relationship between these deficits has not been characterized with psychometrically matched tasks. The authors administered 2 visual discrimination and 6 recognition tasks to 43 schizophrenia spectrum patients and 22 nonpsychiatric subjects. When performing difficulty-matched tasks, spectrum subjects showed more severe impairments for motion compared with form processing. When tasks were matched on true score variance, spectrum subjects exhibited worse performance on both form and motion discrimination, and a differential deficit in motion recognition with a short display duration and long interstimulus interval. These results provide evidence of differential deficits in visual processing in schizophrenia that appear to be dependent on the temporal characteristics of the tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal processing in the basal ganglia.

This study investigated the role of the basal ganglia in timing operations. Nondemented, medicated Parkinson's disease (PD) patients and controls were tested on 2 motor-timing tasks (paced finger tapping at a 300- or 600-ms target interval), 2 time perception tasks (duration perception wherein the interval between the standard tone pair was 300 or 600 ms), and 2 tasks that controlled for the auditory processing (frequency perception) demands of the time perception task and the movement rate (rapid tapping) in the motor-timing task. Using A. M. Wing and A. B. Kristofferson's (1973) model, the total variability in motor timing was partitioned into a clock component, which reflects central timekeeping operations, and a motor delay component, which estimates random variability due to response implementation processes. The PD group was impaired at both target intervals of the time perception and motor-timing tasks. Impaired motor timing was due to elevated clock but not motor delay variability. The findings implicate the basal ganglia and its thalamocortical connections in timing operations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual form discrimination from texture cues: a PET study

With the purpose of localising the cerebral cortical areas participating in the discrimination of visual form generated exclusively by texture cues, we measured changes in regional cerebral blood flow (rCBF) with positron emissions tomography (PET) and 15O-butanol as the tracer. The subjects performed two odd-one-out discrimination tasks: a form-from-texture discrimination task (in which a visual form was defined by differences in texture) and its reference task, the discrimination of texture. During task performance, activated fields were present bilaterally in the primary visual cortex and its immediate extrastriate cortex, the right lateral occipital gyrus, bilaterally in the fusiform and superior temporal gyri and posterior parts of the superior parietal lobules, along the medial bank of the right intraparietal sulcus, and in the right supramarginal gyrus. Other fields were found in the cingulate and prefrontal cortex. The findings demonstrate that the discrimination of visual form as defined by texture engages cortical fields that are widely distributed ion the human brain. In the visual cortex, the activated fields are present in both the occipito-temporal and occipito-parietal visual areas. These results suggest that the perception and discrimination of forms in the visual system requires the joint-activation of neuronal populations in the visual cortex.     

The neuronal machinery involved in successive orientation discrimination

Following our strategy of using simple discrimination tasks to investigate the primate visual system, we trained both human and monkey subjects for two orientation discrimination tasks: an identification and a successive discrimination. Contrasting these two tasks allowed us to isolate the temporal comparison component and to relate this component to activity in right fusiform gyrus using Positron Emission Tomography (PET) and to infero-temporal cortex using a lesion approach in monkeys. Single-cell recordings in infero-temporal cortex demonstrated that neurons in this region can contribute to the three processes underlying temporal comparison: (1) sensorial representation of visual stimuli, (2) maintaining a trace of the preceding stimulus, and (3) comparison of the incoming stimulus with that trace. By the same token, a comparison of these two tasks, which use the same input and the same attribute, demonstrates the task dependency of processing in the human and non-human primate visual system.     

Auditory information processing during acute insulin-induced hypoglycaemia in non-diabetic human subjects

Acute insulin-induced hypoglycaemia impairs performance on tests of general mental ability in humans. It is recognized that different brain functions vary in their sensitivity to neuroglycopenia, but little is known about the effects of neuroglycopenia on specific brain processes. The effect of controlled hypoglycaemia on two aspects of auditory information processing (auditory temporal processing and simple auditory processing) was examined in a homogeneous group of 20 healthy non-diabetic human subjects. Auditory temporal processing (temporal order discrimination) and simple auditory processing (pitch discrimination, single-tone duration and single-tone loudness discrimination) tests were part of the Test of Basic Auditory Capabilities (TBAC). Two tests of general cognitive performance (Digit Symbol Substitution and Trail Making B) were included to provide a measure of general brain functioning during hypoglycaemia. Hypoglycaemia lead to a significant deterioration in auditory temporal processing (P < 0.01), and a deterioration in one of three tasks of simple auditory processing (discrimination of single-tone loudness, P < 0.05). Significant disruptions also occurred in both tests of general brain functioning. These results are congruent with other studies in human subjects, showing a disruptive effect of hypoglycaemia on visual information processing when examined under conditions of limited perceptual time, and they provide further evidence of the importance of sensory processing speed in basic perceptual and cognitive functions. The disruptive effect of moderate insulin-induced hypoglycaemia on auditory perception may have implications for insulin-treated diabetic humans exposed to this metabolic stress, because of the importance of hearing in everyday life.     

Parallel processing streams in human visual cortex

This study shows the existence in humans of independent neural processing streams in early visual cortex, which had previously been demonstrated in macaque monkeys. This evidence was obtained by controlled fixation testing of a subject who had suffered a small stroke in the right fusiform gyrus. The patient showed a severe disruption of color perception, shape discrimination and contrast sensitivity for stationary gratings in the upper left quadrant of his visual field. However, motion perception and contrast sensitivity for drifting gratings were relatively preserved. These results support the view that there are independent visual processing streams early in human visual cortex, and that these streams may subserve such functions as motion and color/form perception.     

Integrating art historical, psychological, and neuroscientific explanations of artists' advantages in drawing and perception.

Art historians, artists, psychologists, and neuroscientists have long asserted that artists perceive the world differently than nonartists. Although empirical research on the nature and correlates of skilled drawing is limited, the available evidence supports this view: artists outperform nonartists on visual analysis and form recognition tasks and their perceptual advantages are correlated with and can be largely accounted for by drawing skill. The authors propose an integrative model to explain these results, derived from research in psychology and cognitive neuroscience on how category knowledge, attention, and motor plans influence visual perception. The authors claim that (a) artists' specialized, declarative knowledge of the structure of objects' appearances and (b) motor priming achieved via proceduralization and practice in an artistic medium both contribute to attention-shifting mechanisms that enhance the encoding of expected features in the visual field and account for artists' advantages in drawing and visual analysis. Suggestions for testing the model are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extent and limits of callosal plasticity: presence of disconnection symptoms in callosal agenesis

Although earlier studies have emphasized the absence of 'split-brain' symptoms in callosal agenesis patients, the notion of an 'asymptomatic' acallosal brain has lately been challenged. We report a number of findings that are indicative of an interruption of interhemispheric communication and integration in individuals lacking the corpus callosum. Several groups of patients with callosal pathology (acallosals, patients with commissurotomy or callosotomy, either complete or partial) were compared to matched controls. Interhemispheric transfer was tested in two different experiments involving pointing to a light source while maintaining central fixation. In the first experiment, a learning paradigm was used to measure transfer of a motor skill from the trained to the untrained hand. In the second experiment, subjects pointed to visual targets at different locations on a perimeter. Midline fusion, a recurrent theme when describing callosal function, was assessed using tasks which included depth perception with binocular and/or monocular cues, two-point discrimination thresholds and sound localization in the peri-central and lateral fields. Subjects with callosal pathology were impaired on all tasks involving transfer of motor and visuo-spatial skills and on some of the tasks requiring sensory integration of visual and tactile information across the body midline. We conclude that these functions require an intact corpus callosum since none of these deficits were seen in controls equated for IQ.     

When writing impairs reading: Letter perception’s susceptibility to motor interference.

The effect of writing on the concurrent visual perception of letters was investigated in a series of studies using an interference paradigm. Participants drew shapes and letters while simultaneously visually identifying letters and shapes embedded in noise. Experiments 1–3 demonstrated that letter perception, but not the perception of shapes, was affected by motor interference. This suggests a strong link between the perception of letters and the neural substrates engaged during writing. The overlap both in category (letter vs. shape) and in the perceptual similarity of the features (straight vs. curvy) of the seen and drawn items determined the amount of interference. Experiment 4 demonstrated that intentional production of letters is not necessary for the interference to occur, because passive movement of the hand in the shape of letters also interfered with letter perception. When passive movements were used, however, only the category of the drawn items (letters vs. shapes), but not the perceptual similarity, had an influence, suggesting that motor representations for letters may selectively influence visual perception of letters through proprioceptive feedback, with an additional influence of perceptual similarity that depends on motor programs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in audiovisual discrimination learning by Bengalese Finches (Lonchura striata var. domestica).

Both visual and auditory information are important for songbirds, especially in developmental and sexual contexts. To investigate bimodal cognition in songbirds, the authors conducted audiovisual discrimination training in Bengalese finches. The authors used two types of stimulus: an "artificial stimulus," which is a combination of simple figures and sound, and a "biological stimulus," consisting of video images of singing males along with their songs. The authors found that while both sexes predominantly used visual cues in the discrimination tasks, males tended to be more dependent on auditory information for the biological stimulus. Female responses were always dependent on the visual stimulus for both stimulus types. Only males changed their discrimination strategy according to stimulus type. Although males used both visual and auditory cues for the biological stimulus, they responded to the artificial stimulus depending only on visual information, as the females did. These findings suggest a sex difference in innate auditory sensitivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual information processing in high-functioning individuals with autism spectrum disorders and their parents.

The authors assessed visual information processing in high-functioning individuals with pervasive developmental disorders (PDD) and their parents. The authors used tasks for contrast sensitivity, motion, and form perception to test visual processing occurring relatively early and late in the magnocellular-dorsal and parvocellular-ventral pathways. No deficits were found in contrast sensitivity for low or high spatial frequencies or for motion or form perception between individuals with PDD in comparison with a matched control group. Individuals with PDD performed equally with or better than controls on motion detection tasks. In addition, the authors did not find differences on any of the tasks between parents of the PDD group and matched control parents. These results indicate that high-functioning individuals with PDD and their parents are able to process visual stimuli that rely on early or late processing in the magnocellular-dorsal and parvocellular-ventral pathways as well as controls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

There's more to colour than meets the eye

Patients with cerebral achromatopsia, a perceptual disorder caused by ventromedial occipital brain damage, can be completely unable to arrange colours in chromatic sequence and fail most conventional tests of colour blindness. A possible explanation for cerebral achromatopsia is that the colour-opponent parvocellular (P) channel has been selectively and totally destroyed at the level of visual cortex, leaving vision to be mediated by the broad-band magnocellular (M) channel. The persistence of normal occipital visually evoked potentials, and preserved sensitivity to isoluminant chromatic gratings indicates that if this hypothesis is correct the destruction must occur beyond the striate cortex. We have shown that an achromatopsic subject can detect chromatic borders and construct shape from colour, and that he can even perceive the apparent direction of motion of a phase shifted isoluminant chromatic grating where perceived direction depends on knowing the sign of the colour diffence, i.e., which colour is which in the stripes. This and other evidence suggests that perhaps only one part of the cortical P channel has been destroyed. Does the critical area involved in achromatopsia correspond to cortical area V4 of monkeys, often implicated in processing wavelength? When Visual Area 4 is totally ablated in monkeys they have only a mild colour discrimination impairment and easily solve the colour ordering and colour selection tasks that an achromatopsic patient finds impossible. However, monkeys with ventromedial damage rostral to Area V4 do perform like achromatopsic patients, suggesting that the role of V4 in the perception of colour is still unclear and that the colour area of the human brain does not correspond to area V4.     

Role of gamma-band synchronization in priming of form discrimination for multiobject displays.

Previous research has shown that synchronized flicker can facilitate detection of a single Kanizsa square. The present study investigated the role of temporally structured priming in discrimination tasks involving perceptual relations between multiple Kanizsa-type figures. Results indicate that visual information presented as temporally structured flicker in the gamma band can modulate the perception of multiple objects in a subsequent display. For judgments of both relative orientation and relative position of 2 rectangles, response time to identify and discriminate relations between the objects was consistently decreased when the vertices corresponding to distinct Kanizsa-type rectangles were primed asynchronously. Implications are discussed for models of the perception of objects and their interrelations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The effects of V4 and middle temporal (MT) area lesions on visual performance in the rhesus monkey

The effects of V4, MT, and combined V4 + MT lesions were assessed on a broad range of visual capacities that included measures of contrast sensitivity, wavelength and brightness discrimination, form vision, pattern vision, motion and flicker perception, stereopsis, and the selection of stimuli that were less prominent than those with which they appeared in stimulus arrays. The major deficit observed was a loss in the ability, after V4 lesions, to select such less prominent stimuli; this was the case irrespective of the manner in which the stimulus arrays were made visible, using either luminance, chrominance, motion, or stereoscopic depth as surface media. In addition, V4 lesions yielded mild deficits in color, brightness, and form vision whereas MT lesions yielded mild to moderate deficits in motion and flicker perception. Both lesions produced mild deficits in contrast sensitivity, shape-from-motion perception, and yielded increased reaction times on many of the tasks. The impairment resulting from combined V4 and MT lesions was not greater than the sum of the deficits of either lesion. None of the lesions produced significant deficits in stereopsis. The findings suggest that (1) area V4 is part of a neural system that is involved in extracting stimuli from the visual scene that elicit less neural activity early in the visual system than do other stimuli with which they appear and (2) several other extrastriate regions and more than just two major cortical processing streams contribute to the processing of basic visual functions in the extrastriate cortex.     

Effects of early experience on children's recognition of facial displays of emotion.

The present research examines visual perception of emotion in both typical and atypical development. To examine the processes by which perceptual mechanisms become attuned to the contingencies of affective signals in the environment, the authors measured the sequential, content-based properties of feature detection in emotion recognition processes. To evaluate the role of experience, they compared typically developing children with physically abused children, who were presumed to have experienced high levels of threat and hostility. As predicted, physically abused children accurately identified facial displays of anger on the basis of less sensory input than did controls, which suggests that physically abused children have facilitated access to representations of anger. The findings are discussed in terms of experiential processes in perceptual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Independent practice association physician groups in California

Hemispatial neglect is a neurological disorder which entails a spatial bias that penalizes events occurring in the hemispace contralateral to a brain lesion. Mechanisms operating upon various stages ranging from perception to action have been invoked to explain neglect. The present study explores the contribution of a defective programming of arm movements towards the neglected hemispace to neglect behaviour. Two reaction time tasks -- a "perceptual" task and a "motor" task -- were performed by right brain-damaged (RBD) patients with left hemispatial neglect, RBD patients without signs of neglect and control subjects. The perceptual task consisted of lateralized visual stimuli and central motor responses, whereas the motor task consisted of visual stimuli presented on the vertical midline and hand responses to be produced in either hemispace. Neglect patients showed a rightward bias on the perceptual task, but only two RBD patients (showing no signs of severe neglect) were consistently slowed in producing leftward motor responses. Different reference frames may thus be used in perceptual tasks and tasks involving arm movements. We conclude that hemispatial neglect commonly results from attentional impairments operating upon a visual perceptual frame of reference; additional deficits appear to be necessary to produce a directional motor disorder.     

Feedback analysis of learning and performance in steering and tracking behavior.

Tested the assumption that steering and tracking behavior are interrelated in terms of the extent of self-produced stimulation involved in the 2 tasks. Steering was defined as involving maximal, and stimulus tracking as involving minimal levels of movement-regulated sensory information. 3 tasks steering, as governed by breath-produced target movement, stimulus tracking, and a hand-yoked target control task were compared under conditions in which the difficulty of the steering and stimulus tracking tasks were exactly equated. Results show that steering performance was more accurate and learned more rapidly than stimulus tracking. Oscillograph records of all aspects of performance indicate that the 2 tasks differed psychophysiologically in terms of how the self-timed respiratory activities and the external manual-visual responses were continuously and dynamically interrelated to control visual input. Results suggest that the modes and conditions of feedback control of dynamic sensory input not only determine accuracy of performance and rate of learning, but also define how internally-timed organic functions are integrated to determine learning in motor skills and other activities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)