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PubMed2004

Depth perception from second-order-motion stimuli yoked to head movement.

We examined whether depth perception was produced by the parallax of second-order motion (i.e., movement of non-luminance features, such as flicker, texture size modulation, or contrast modulation that moved in synchrony with lateral head movement). The results, obtained with second-order motion from a simple grating stimuli, showed that depth order was judged correctly with probabilities well above chance, but the reported depth magnitude did not co-vary with parallax magnitude. When we used a complex spatial pattern for which feature tracking was difficult, the accuracy of depth-order judgments descended to chance level. Our results suggest that the visual system (a) can detect the correct depth order by tracking a relative shift in the salient features of a stimulus pattern, but (b) cannot determine depth magnitude from a velocity field given by second-order-motion stimuli.

Cues↗
PubMed1992

Clinical measurement of depth perception by means of motion parallax: a case report.

An automated 2-rod stereoacuity test was modified to permit lateral head movement during testing so that depth perception by means of motion parallax could be assessed. The patient, a 48-year-old truck driver with one blind eye, found the test easy to perform. In 24 presentations of a 40 sec arc disparity he was 96% correct. With the same number of presentations at 20 sec arc he was 83% correct. In the latter case, the probability of success by chance alone was p = 0.0004.

Depth Perception↗
PubMed1992

Coherence and transparency of moving plaids composed of Fourier and non-Fourier gratings.

We examined the perceptual coherence of two-component moving plaids. The gratings that constituted the plaids were either standard Fourier gratings (F), in which luminance was determined by a drifting sinusoid, or non-Fourier gratings (NF), in which the contrast of a random background was modulated by a drifting sinusoid. These NF gratings are examples of stimuli that generate a compelling percept of motion, even though they fail to elicit a motion signal from motion analyzers based on standard cross-correlation (Chubb & Sperling, 1988). Naive observers viewed three types of stimuli consisting of superpositions of these two components: (1) two standard drifting gratings (F/F), (2) two non-Fourier drifting gratings (NF/NF), and (3) one standard and one non-Fourier drifting grating (F/NF). As expected, the F/F stimulus yielded a compelling percept of coherent motion. The dominant percept of all the observers for the NF/NF stimulus was one of coherent motion, provided that both gratings were visible and of approximately equal contrast. None of the observers reported a dominant percept of coherent motion for the F/NF condition, over a wide range of contrasts for the two grating components and across two varieties of NF gratings. In view of the results of Albright (1992) and Albright and Chaudhuri (1989), that show that single cells in macaque V1 and MT respond to both F and NF motion, one cannot interpret our findings as evidence that F and NF motion are processed independently. Alternative, "higher level" interpretations based on the intrinsically ambiguous nature of the stimuli and physical laws governing the appearance of transparent objects are discussed.

Adult↗
PubMed1999

Dependence of impaired eye tracking on deficient velocity discrimination in schizophrenia.

BACKGROUND: Abnormal smooth pursuit eye movements have been found in many schizophrenic patients and in about 40% of their first-degree biological relatives. A velocity discrimination deficit has also been demonstrated in schizophrenic patients. In this study, we address the relation between deficient velocity discrimination and impaired smooth pursuit eye movements, inasmuch as the brain regions responsible for processing velocity signals are implicated in generating and maintaining smooth pursuit. METHODS: Horizontal eye movements of 15 schizophrenic patients and 8 normal controls were recorded in response to sine wave (predictable) and step-ramp (nonpredictable) targets. Smooth pursuit eye movements were assessed during both the initiation and maintenance periods. Correlations were computed between measures of smooth pursuit (qualitative rating, peak gain, saccade frequency, and initial acceleration) and contrast sensitivity for velocity discrimination. RESULTS: Contrast sensitivity for fine velocity discrimination was significantly correlated both with initial acceleration of smooth pursuit and with peak gain, but was not significantly correlated with saccade frequency and qualitative ratings of pursuit integrity. No significant correlations were found within the normal control group. CONCLUSION: Deficient processing of velocity information seems to be one component that contributes to a dysfunction in the initiation and maintenance of smooth pursuit in schizophrenia.

Brain↗
PubMed1996

Recognition of visual stimuli from multiple neuronal activity in monkey visual cortex.

Response patterns recorded with 30 microelectrodes from area 17 of anaesthetized monkeys are analysed. A proportion of the patterns are used to define prototype response patterns. These in turn are used to recognize the stimulus from further non-averaged response patterns. In comparison, recognition by a feedforward 'neural network' is much slower, and slightly inferior. The excitation time structure, with a resolution of about 20 ms, is found to contribute strongly to the recognition. There is some inter-ocular recognition for oriented moving bars, and for on and off phases of switched lights, but none for colours. Generalizations over some stimulus parameters (i.e. cases of confusion) are examined: If small jerking shapes are incorrectly recognized, in general the jerk direction often is the correct one. The onset of a response can most easily be found by determining the dissimilarity relative to spontaneous activity in a sliding window.

Animals↗
PubMed1986

Testing visual perception of three-dimensionally moving objects (dynamic stereoscopy).

In the past decade, visual requirements in the field of stereoscopy have considerably increased in a number of professions, as well in present-day traffic and sports. As a result of a statement of the WHO (1984) viz. that for prevention of accidents the testing of static vision only is insufficient, and that dynamic vision too should be a subject of investigation, a test for measuring dynamic stereoscopic visual acuity has been devised. With the help of two synchronously rotating prisms, a stereo test consisting of four bars is transposed into an apparent circumduction movement which is presented at different velocities. Stereoscopy under static and dynamic conditions do not run a parallel course. Dynamic stereoscopy is significantly influenced by age, but not by sex.

Adult↗
PubMed1990

Areal influences on complex cells in cat striate cortex: stimulus-specificity of width and length summation.

In single neurones recorded from the striate cortex of cats anaesthetized with N2O/O2/halothane, receptive field dimensions, length specificity and areal extent of drive were assessed for different classes of visual stimuli. Receptive fields were mapped as rectangular minimum response fields (MRFs). Spatial summation along the axis of preferred orientation was assessed: for moving bars whose length was varied (length summation); and for height variation of a square-wave grating patch against a uniform grey background, or a patch of moving texture against a stationary background of similar texture. In complementary tests a moving square-wave grating background was progressively occluded by a uniform grey foreground mask of variable height; or a mask of stationary texture of variable height progressively occluded a background of moving texture. In parallel measurements, the width of grating or textured patches or masks was varied whilst maintaining height constant. Broadly speaking, the areal influence of each class of stimulus was comparable, and distinct from extra-receptive field phenomena in evoking responses from within the receptive field, but not from surrounding areas. The masking paradigm provided the most sensitive measure of receptive field height and width. However, in some neurones length summation, the degree of end-stopping, and the directional bias depended critically on the stimulus configuration used. Length summation tended to be more dramatic for short bars than for gratings. Length summation for texture was significantly more pronounced than for an oriented bar in special and in intermediate complex neurones. By contrast, endstopping was typically less intense for gratings than for bars, and least pronounced for texture. Because of stimulus specificity, complex neurones assigned to particular functional subgroups on the basis of their response to oriented bars may exhibit quite different patterns of behaviour for other classes of stimuli.

Animals↗
PubMed1993

The suppression of cervico-ocular response by the haptokinetic information about the contact with a rigid, immobile object.

Horizontal eye movements were recorded in eight healthy subjects during super-slow trunk rotation with respect to the space-stationary head. In some trials, subjects simultaneously indicated their perception of self-motion by means of a joystick. Over the frequency range employed (0.007-0.05 cycles per second, +/- 20 degrees), all subjects perceived the relative motion of head and trunk as a head rotation with respect to the stationary trunk. Eye movements were observed which were in phase with imaginary head rotation; their amplitude exceeded the amplitude of actual body rotation. The grasping of a rigid ground-based handle (1) produced a sensation of trunk rotation in space, (2) suppressed the sensation of imaginary head rotation in space and (3) gave rise to a significant decrease in amplitude of eye movements. The grasping of a stiff rod with non-zero compliance did not produce these effects. It is concluded that eye movements in response to body rotation with respect to the fixed head are not purely reflex reactions, but are influenced by the internal representation of body motion.

Eye Movements↗
PubMed1975

Responses of striate cortical cells to moving edges of different curvatures.

The responses of twenty cells to stimuli of varying curvature were measured in cat's striate cortex. All the investigated cells were sensitive to the orientation of lines and not hypercomplex. Fourteen cells showed a systematic change of response with curvature. The optimal curvatures of the cells were distributed over the whole range investigated. Six cells were insensitive to curvature. The responses from all the typical simple cells (8) varied with curvature, whereas all the complex cells (5) were insensitive to curvature changes. The curvature tuning curves were broad and the variability to individual stimuli was high, independent on whether the cell responded best to straight or to curved edges. The findings do not support the view that individual cells of area 17 could detect curvature.

Animals↗
PubMed1986

Visual properties and spatial distribution of neurones in the visual association area on the prelunate gyrus of the awake monkey.

We have analysed, in the awake monkey (Macaca sylvana) the functional properties of 489 neurones in the prelunate visual area (PVA, largely corresponding to V4). PVA has a coarse retinotopic organization with the lower quadrant of the visual field represented along the prelunate gyrus. The visual periphery is located medio-dorsally, the central visual field laterally near (and within?) the inferior occipital sulcus and the upper quadrant latero-ventrally. The vertical meridian runs caudally within the lunate sulcus, the horizontal meridian crosses the prelunate gyrus and continues into the superior temporal sulcus. Receptive field diameters of neurones vary between 1 degree and 10 degrees with increase towards the visual periphery, but are strictly confined to the contralateral visual field. 28% of the neurones showed spectral sensitivity. About half of these cells had strong spectral opponency, the other half showed only weak opponency with broader spectral response curves. 11 cells (2%) showed striking centre/surround interactions with inhibition, disinhibition or occlusion of the two mechanisms, and different spectral response ranges of the centre and the surround, respectively. 43% of the prelunate cells were responsive to various spatial features without spectral sensitivity. We distinguished on- and off-center cells (2%), direction and movement sensitive cells (10%) and cells sensitive to gratings of parallel lines within a limited range of orientations (about 10%). A special group were cells which responded strongly to stimuli which contained many contrasts (textures without specific orientations and without regular spatial arrangements) (9%). Many of these cells were specifically responsive to variations of the internal structure of such stimuli. 3% of the cells were strongly activated in connection with behaviour: 11 neurones discharged strongly when the monkey looked attentively at a human face or when he responded with facial expressions to a threatening expression of a person. Photographs of faces were not effective. Some neurones (1%) were activated in connection with eye movement. These neurones were found in the lateral part of the prelunate gyrus. Neurones with spectral or non-spectral properties were clustered within small, irregularly shaped patches of 1-4 mm diameter. It is concluded that the prelunate visual cortex, which we consider as part of area 19, is not just a "colour area", but represents various features of the visual environment (including colour, luminance, movement, texture and behavioral significance), and relates them - through its subcortical and cortical outputs - to behaviour.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Object-centered encoding by face-selective neurons in the cortex in the superior temporal sulcus of the monkey.

Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and in the inferior temporal cortex respond to faces. To determine if some face responsive neurons encode stimuli in an object-centered coordinate system rather than a viewer-centered coordinate system, a large number of neurons were tested for sensitivity to head movement in 3 macaque monkeys. Ten neurons responded only when a head undergoing rotatory movements was shown. All of these responded to a particular movement independently of the orientation of the moving head in relation to the viewer, maintaining specificity even when the moving head was inverted or shown from the back, thereby reversing viewer-centered movement vectors. This was taken as evidence that the movement was encoded in object-centered coordinates. In tests of whether there are neurons in this area which respond differently to the faces of different individuals relatively independently of viewing angle, it was found that a further 18 neurons responded more to one static face than another across different views. However, for 16 of these 18 cells there was still some modulation of the neuronal response with viewing angle. These 16 neurons thus did not respond perfectly in relation to the object shown independently of viewing angle, and may represent an intermediate stage between a viewer-centered and an object-centered representation. In the same area as these neurons, other cells were found which responded on the basis of viewer-centered coordinates. These neurophysiological findings provide evidence that some neurons in the inferior temporal visual cortex respond to faces (or heads) on the basis of object-centered coordinates, and that others have responses which are intermediate between object-centered and viewer-centered representations. The results are consistent with the hypothesis that object-centered representations are built in the inferior temporal visual cortex.

Animals↗
PubMed1989

Considerable deficits in the detection performance of the cat after lesion of the suprasylvian visual cortex.

The ability of two cats to discriminate between two geometrical outline patterns in the presence of superimposed structured background was tested before and after bilateral removal of the lateral suprasylvian visual areas (PMLS, PLLS, AMLS, ALLS, part of area 7). There were mild deficits when patterns and background were kept stationary; these deficits may be due to a partial undercutting of areas 17, 18 and 19. However, there was a severe impairment in performance when the patterns were moving on a stationary background which may be due to loss of the suprasylvian visual areas. Movement of the background relative to the figure resulted in an intermediate detection deficit.

Animals↗
PubMed1982

Visibility of movement gradients.

We report on the sensitivity of human observers with respect to the detection of transients in otherwise uniformly moving two-dimensional random-dot patterns. The target field is divided into two halfs that each contains a moving random-dot pattern. The patterns in the two halffields are mutually uncorrelated. Parameters are the average velocity and the difference-velocity for the two halfs. These velocities are both vectors that can be varied in magnitude and in their direction with respect to the border of the two halffields. In order to quantify the sensitivity of the visual system to such patterns, we added (linear addition) spatio-temporal white noise ("snow") to the pattern. Then the sensitivity is quantified by way of the threshold signal-to-noise ratio necessary to discriminate the composite pattern from a single smoothly uniformly moving pattern. The signal-to-noise ratio specifies the square of the ratio between the signal r.m.s. contrast and the r.m.s. contrast of the masking stimulus (spatio-temporal white noise or "snow"). The r.m.s. contrast of the complex pattern (signal and noise) is kept invariant. We find that the detection performance is independent of the direction of either the average of difference-velocity with respect to the border, and can be completely described in terms of a minimum requirement for the magnitude of the difference-velocity. The magnitude of the difference-velocity must exceed the magnitude of the average velocity in order to lead to a perceivable transient. In this formulation the Weberlaw for the detection of velocity transients in uniformly moving noise patterns is applicable to both differences in magnitude and direction of the velocities.

Discrimination Learning↗