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PubMedDate not supplied

Organization of ocular dominance and orientation columns in the striate cortex of neonatal macaque monkeys.

Previous work has shown that small, stimulus-dependent changes in light absorption can be used to monitor cortical activity, and to provide detailed maps of ocular dominance and optimal stimulus orientation in the striate cortex of adult macaque monkeys (Blasdel & Salama, 1986; Ts'o et al., 1990). We now extend this approach to infant animals, in which we find many of the organizational features described previously in adults, including patch-like linear zones, singularities, and fractures (Blasdel, 1992b), in animals as young as 3 1/2 weeks of age. Indeed, the similarities between infant and adult patterns are more compelling than expected. Patterns of ocular dominance and orientation, for example, show many of the correlations described previously in adults, including a tendency for orientation specificity to decrease in the centers of ocular dominance columns, and for iso-orientation contours to cross the borders of ocular dominance columns at angles of 90 deg. In spite of these similarities, there are differences, one of which entails the strength of ocular dominance signals, which appear weaker in the younger animals and which increase steadily with age. Another, more striking, difference concerns the widths of ocular dominance columns, which increase by 20% during the first 3 months of life. Since the cortical surface area increases by a comparable amount, during the same time, this 20% expansion implies that growth occurs anisotropically, perpendicular to the ocular dominance columns, as the cortical surface expands. Since the observed patterns of orientation preference expand more slowly, at approximately half this rate, these results also imply that ocular dominance and orientation patterns change their relationship, and may even drift past one another, as young animals mature.

Aging↗

PubMedDate not supplied

Spatial-frequency and orientation tuning in psychophysical end-stopping.

A psychophysical analog to cortical receptive-field end-stopping has been demonstrated previously in spatial filters tuned to a wide range of spatial frequencies (Yu & Levi, 1997a). The current study investigated tuning characteristics in psychophysical spatial filter end-stopping. When a D6 (the sixth derivative of a Gaussian) target is masked by a center mask (placed in the putative spatial filter center), two end-zone masks (placed in the filter end-zones) reduce thresholds. This "end-stopping" effect (the reduction of masking induced by end-zone masks) was measured at various spatial frequencies and orientations of end-zone masks. End-stopping reached its maximal strength when the spatial frequency and/or orientation of the end-zone masks matched the spatial frequency and/or orientation of the target and center mask, showing spatial-frequency tuning and orientation tuning. The bandwidths of spatial-frequency and orientation tuning functions decreased with increasing target spatial frequency. At larger orientation differences, however, end-zone masks induced a secondary facilitation effect, which was maximal when the spatial frequency of end-zone masks equated the target spatial frequency. This facilitation effect might be related to certain types of contour and texture perception, such as perceptual pop-out.

Adult↗

PubMedDate not supplied

The sensitivity of neurons in the lateral geniculate body of the cat to the orientation vectors of brightness gradients.

We describe here a new property of visual neurons: sensitivity to the magnitude and orientation of the brightness gradient vector in a test stimulus presented in the receptive field of the neuron. The brightness gradient test image was a spot (diameter 4 degrees) on the dark background of the slide. Brightness changed linearly within the spot. The absolute value of the brightness gradient varied over the range 0.4-2.7 cd/m2 /degrees in the direction of the brightness gradient. The integral brightness in the test spot containing the gradient image was identical for different values of the brightness gradient. The numbers of spikes in the on- and off-responses of on and off neurons in the lateral geniculate body of cats depended on the orientation of the brightness gradient vector in the test stimulus. The sensitivity of neurons to the orientation of the brightness gradient vector, K (the coefficient of sensitivity), was assessed as the normalized difference between the number of spikes in neuron responses in the preferred and non-preferred orientations of the brightness gradient vector in the neuron's receptive field. The mean sensitivity coefficient for 53 cells was 0.55 +/- 0.20. A 6.7-fold decrease in the brightness gradient resulted in a 3.7-fold decrease in the coefficient of sensitivity (for the preferred direction of the orientation of the gradient vector); there was no change in the latent period of responses. The preferred orientation of the brightness gradient vector in the receptive fields of neurons coincided (to within +/-22.5 degrees) with the radial direction on the map of the field of vision in 45% of cases, and with the tangential direction in 26% of cells.

Animals↗

PubMed1998

Children with autism fail to orient to naturally occurring social stimuli.

Children with autism were compared to developmentally matched children with Down syndrome or typical development in terms of their ability to visually orient to two social stimuli (name called, hands clapping) and two nonsocial stimuli (rattle, musical jack-in-the-box), and in terms of their ability to share attention (following another's gaze or point). It was found that, compared to children with Down syndrome or typical development, children with autism more frequently failed to orient to all stimuli, and that this failure was much more extreme for social stimuli. Children with autism who oriented to social stimuli took longer to do so compared to the other two groups of children. Children with autism also exhibited impairments in shared attention. Moreover, for both children with autism and Down syndrome, correlational analyses revealed a relation between shared attention performance and the ability to orient to social stimuli, but no relation between shared attention performance and the ability to orient to nonsocial stimuli. Results suggest that social orienting impairments may contribute to difficulties in shared attention found in autism.

Attention↗

PubMed1978

Orientation and symmetry: effects of multiple, rotational, and near symmetries.

Time to detect bilateral symmetry in different orientations was studied for closed polygons with single, double, quadruple, rotational, and near symmetry. In Experiment 1, the orientation of the axis of symmetry was varied. Detection was fastest for vertical symmetry, next fastest for horizontal, and slowest for left- and right-diagonal symmetries. For corresponding orientations, responses were faster to quadruple than double symmetries, and faster to double than single symmetries. Negative responses to nearly symmetric figures produced an orientation effect similar to that for single symmetries. Rotational symmetries showed no orientation effect and took longer to reject than near symmetries. In Experiment 2, subjects looked only for vertical symmetry. Responses were twice as fast as in comparable conditions of Experiment 1. The effect of multiple symmetries was still present, but rotational symmetries were rejected faster than near symmetries. The results are interpreted as supporting a dual process model for detecting symmetry in multiple orientation channels: Observers first select potential axes of symmetry defined by mirror-similar parts and then evaluate specific axes sequentially in a detailed comparison for mirror-identity.

Form Perception↗

PubMed1987

Cognitive maps as orienting schemata.

A "point-to-unseen-targets" task was used to test two theories about the nature of cognitive mapping. The hypothesis that a cognitive map is like a "picture in the head" predicts that (a) the cognitive map should have a preferred orientation and (b) all coded locations should be equally available. These predictions were confirmed in Experiments 1 and 3 when targets were cities in the northeastern United States and learning was from a map. The theory that a cognitive map is an orienting schema predicts that the cognitive map should have no preferred orientation and that targets in front of the body should be localized faster than targets behind the body. These predictions were confirmed in Experiments 1 and 2 when targets were local landmarks that had been learned via direct experience. In Experiment 3, when cities in the Northeast were targets and geographical knowledge had been acquired, in part, by traveling in the Northeast, the observed latency profiles were not as predicted by either theory of cognitive mapping. The results suggest that orienting schemata direct orientation with respect to local environments, but that orientation with respect to large geographical regions is supported by a different type of cognitive structure.

Attention↗

PubMed2002

The role of self-to-object updating in orientation-free performance on spatial-memory tasks.

A single view of a room-sized path produces an orientation-specific memory representation, yet when memory is tested at a location on the path, orientation-free performance is observed. Either a virtual-views or an updating hypothesis can account for orientation-free performance by attributing it, respectively, to an orientation-free long-term-memory representation or to a working-memory representation of the body's updated location relative to the path. Experiments 1 and 2 test these hypotheses by manipulating the test-site location and the complexity of the trajectory from the study site to the test site. Experiment 3 tests orientation to the test space as a function of trajectory complexity. Results support a virtual-views explanation for the orientation-free performance of males and an updating explanation for females.

Adolescent↗

PubMed2004

Interactions between phasic alerting and spatial orienting: effects of normal aging and Alzheimer's disease.

The effects of aging and Alzheimer's disease (AD) on phasic alerting and exogenous spatial orienting were examined within a single precuing task. Phasic alerting decreased with normal aging and was completely eliminated with AD. AD patients also demonstrated an increased spatial orienting effect, attributable to an increased benefit from spatial orienting that was associated with a decreased benefit from nonselective alerting. These results suggest that performance within the precuing paradigm reflects the product of an interaction between nonselective alerting processes and spatially selective orienting processes. The results also highlight the importance of simultaneously assessing alerting and orienting within the same task, because changes attributable to alerting may otherwise be attributed incorrectly to changes in 1 or more processes associated with spatial orienting.

Adolescent↗

PubMed1988

Inhibition contributes to orientation selectivity in visual cortex of cat.

Neurons in the visual cortex are selectively responsive to light or dark bars presented at particular orientations. On the basis of physiological data, this orientation selectivity is hypothesized as being due at least partially to intracortical inhibitory mechanisms. But this hypothesis has been challenged by intracellular recordings indicating that excitatory inputs themselves are orientation-selective, so inhibition may not contribute to the observed selectivity. Also, there is controversy about the presence of intracortical horizontal connections mediating inhibition for selectivity and about the theoretical validity of such inhibitory connections. Using cross-correlation analysis of the activities of two neurons recorded simultaneously, we find that inhibitory interactions exist between cells with somewhat different, but not orthogonal, orientation preferences. This suggests that intracortical horizontal inhibition operates between 'orientation columns' to sharpen the orientation tuning of cortical neurons.

Action Potentials↗

PubMed2003

Independence of visuotopic representation and orientation map in the visual cortex of the cat.

The representations of visual space and stimulus orientation were mapped in the cat primary visual cortex using electrophysiological recordings supplemented with intrinsic signal optical imaging. The majority of units displaced up to 600 micro m laterally had overlapping RFs both in orientation domains and around singularities of the orientation map. Quantitative comparison of these units revealed only a weak, positive correlation between the difference in their preferred orientations and RF separations (area 17: r = 0.09; area 18: r = 0.15). The occurrence of nonoverlapping RFs could be accounted for by random RF position scatter rather than by orientation difference between the units. Monte Carlo analysis showed that our findings are compatible with a locally smooth and linear representation of visual space that is not coupled to the representation of stimulus orientation. An important functional implication of the above map relationships is that positional information captured by the retina is faithfully transmitted into the cortex.

Animals↗

PubMed1994

The dependence of two-dimensional shape perception on orientation.

While it is true that in daily life we generally recognize objects regardless of their orientation, previous experiments involving novel shapes indicate a decline in recognition when these are tested in altered orientation. Here the question is raised of whether there is a component of shape perception based purely on the geometry of an object, independent of orientation. By means of two tests designed to eliminate awareness of change of orientation, one more stringent than used heretofore, it was found that shape perception is dependent on orientation. The apparent contradiction between these findings and the apparent orientation-free character of recognition in daily life is discussed.

Female↗

PubMed2004

Orientation-selective adaptation during motion-induced blindness.

When a global moving pattern is superimposed on high-contrast stationary or slowly moving stimuli, the latter occasionally disappear for periods of several seconds (motion-induced blindness, MIB). Here, an adaptation paradigm was used to determine if orientation-selective adaptation still occurs for the stimulus that is no longer visible. Two slowly drifting high-contrast Gabor patches were presented to observers. As soon as both patches disappeared, one was eliminated from the screen. After 2 s, two low-contrast Gabor patches were presented as tests at the same locations and observers were asked to report their orientations. The observers' performance was significantly higher when the orientation of the low-contrast test patch was orthogonal to the orientation of the high-contrast adapting patch (p < 0.0001) for the location where the patch was present during MIB, even though it was perceptually invisible. The observers' performance was not significantly different at the adjacent control location where the stimulus was absent during the MIB. Although no stimulus was visible at either location, orientation-selective adaptation was preserved only for the location at which the patch remained present. Since orientation information is processed in low-level visual areas such as the primary visual cortex (V1), we conclude that MIB originates in an area higher than V1.

Adaptation, Psychological↗

PubMed2002

Spatial frequency and orientation tuning dynamics in area V1.

Spatial frequency (SF) and orientation tuning are intrinsic properties of neurons in primary visual cortex (area V1). To investigate the neural mechanisms mediating selectivity in the awake animal, we measured the temporal dynamics of SF and orientation tuning. We adapted a high-speed reverse-correlation method previously used to characterize orientation tuning dynamics in anesthetized animals to estimate efficiently the complete spatiotemporal receptive fields in area V1 of behaving macaques. We found that SF and orientation tuning are largely separable over time in single neurons. However, spatiotemporal receptive fields also contain a small nonseparable component that reflects a significant difference in response latency for low and high SF stimuli. The observed relationship between stimulus SF and latency represents a dynamic shift in SF tuning, and suggests that single V1 neurons might receive convergent input from the magno- and parvocellular processing streams. Although previous studies with anesthetized animals suggested that orientation tuning could change dramatically over time, we find no substantial evidence of dynamic changes in orientation tuning.

Animals↗

PubMed2006

Dynamic properties of orientation discrimination assessed by using classification images.

Recent physiological studies indicate that the tuning properties of neurons under acute preparation in primary visual cortex can change over time. We used a psychophysical reverse correlation paradigm to examine the potential repercussions of this neuronal property for human observers' ability to discriminate the orientation of targets over time. Observers were required to identify the orientation of a Gabor target presented within dynamic white noise. Frames from the noise movies were pooled to compute dynamic classification images (CIs) associated with the observers' discrimination performance, which then were fit with a weighted difference-of-Gabor function. Best-fitting templates were temporally bandpass, tuned to more oblique orientations than the stimulus but, crucially, did not change over time. The results suggest that the template for orientation discrimination is selected within the first 50 ms of stimulus onset and that, unlike the response of single cells, there is no measurable dynamic component to either orientation or spatial frequency tuning of human orientation discrimination.

Humans↗

PubMed2006

Unequal representation of cardinal vs. oblique orientations in the middle temporal visual area.

A possible neurobiological basis for the "oblique effect" is linked to the finding that more neural machinery is devoted to processing cardinal vs. oblique orientations in primary visual cortex (V1). We used optical imaging to determine whether more territory is devoted to processing horizontal and vertical orientations than oblique orientations in owl monkey middle temporal visual area (MT), a visual area highly sensitive to moving stimuli. We found that more of MT was devoted to representing cardinal than oblique orientations, and that the anisotropy was more prominent in parts of MT representing central vision (< or =10 degrees). Neural responses to orientations of 0 degrees and 90 degrees were also greater than those to 45 degrees and 135 degrees . In comparison, an overrepresentation of cardinal orientations in the representation of central vision in owl monkey V1 was relatively small and inconsistent. Our data could explain the greater sensitivity to motion discrimination when stimuli are moved along cardinal meridians and suggest that the neural machinery necessary to explain the motion oblique effect either originates in MT or is enhanced at this level.

Animals↗

PubMed1997

Grating detection and orientation discrimination in amblyopia.

PURPOSE: We examined whether the misperceptions associated with amblyopic visual perception can be revealed under natural viewing conditions by comparing the ability to detect the presence of a grating with the ability to identify the grating orientation. METHODS: Grating detection and orientation discrimination performance (horizontal versus vertical) were determined, using stimuli that consisted of sinusoidal gratings of fixed contrast (75%) but with variable spatial frequency. A total of four amblyopic subjects (two strabismic and two non-strabismic) and four age-matched normals participated in the experiment. RESULTS: Psychometric functions for grating detection and orientation identification were found to be closely matched in the normal subjects and in all four amblyopic subjects, indicating that orientation could be correctly identified at detection threshold. CONCLUSIONS: The absence of orientation uncertainty in the psychophysical data for the amblyopic observers is not consistent with the several previous reports of spatial aliasing in the central field of amblyopes. Our results suggest that non veridical visual perception in central amblyopic vision can not be revealed under natural viewing conditions by comparing the ability to detect the presence of a grating with the ability to identify its orientation. Possible reasons for the failure of this technique to reveal spatial aliasing in amblyopes are discussed.

Adult↗

PubMed2006

Orientation of the stethoscope around the neck: a random phenomenon or an indicator of cerebral lateralisation? Cross-sectional survey.

This study aimed to determine whether the orientation of the stethoscope when placed around the neck by physicians is a random occurrence or if this represents a lateral preference. A cross-sectional questionnaire survey was conducted, recruiting 186 medical doctors of all grades from the University Hospital of Wales, Cardiff. Stethoscope orientation preference, and seven other measures of lateral preference (handedness, footedness, eyedness, earedness, hand clasping, arm folding, and leg crossing), were assessed. The percentage of right-type, left-type, and indifferent-type orientation for each of the eight lateral preferences was determined, and 60%, 35%, and 5% of participants demonstrated right, left, and indifferent stethoscope orientation types, respectively. Stethoscope orientation preference correlated with handedness, footedness, earedness, and hand-clasping, but not with eyedness, arm-folding, or leg-crossing. Stethoscope orientation preference is not a chance phenomenon and may be an expression of cerebral dominance.

Adult↗

PubMed1991

Does attention have different effects on line orientation and line arrangement discrimination?

Visual search and texture segregation studies have led to the inference that stimuli differing in the orientation of their component line segments can be distinguished without focal attention, whereas stimuli that differ only in the arrangement of line segments cannot. In most of this research, the locus of attention has not been explicitly manipulated. In the first experiment presented here, attention was directed to a relevant peripheral target by a cue presented near the target location or at the fovea. Effects of attention on orientation discrimination were assessed in a two-alternative forced-choice task with targets that were either: (1) lines that slanted obliquely to the right or left, or were horizontal or vertical, or (2) Y-like targets that had a short arm leading obliquely right or left of a vertical line. In some groups, a four-alternative forced-choice test with lines at 0 degree, 45 degrees, 90 degrees, and 135 degrees orientations was used. Discrimination of these targets (i.e. targets that differ in the orientation of component line segments) was only minimally facilitated as the time between the onset of the valid cue and the onset of the target (cue-target stimulus onset asynchrony, SOA) was increased from 0 or 17 msec to 267 msec. In contrast, discrimination of targets that did not differ in the orientation of component line segments but differed in line arrangement (T-like characters), was greatly facilitated by longer cue-target SOAs. In Experiment 2, a cue misdirected attention on 20% of the trials. A decrement occurred on incorrectly cued trials in comparison to correctly cued trials for both types of stimuli used (lines and Ts). The results from these experiments suggest that discrimination of line orientation benefits less from focal attention than does discrimination of line arrangement, but that both discriminations suffer when attention must be disengaged from an irrelevant spatial location.

Adult↗