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PubMed2001

Vestibular compensation and orientation during locomotion.

Body, head, and eye movements were studied in three dimensions while walking and turning to determine the role of the vestibular system in directing gaze and maintaining spatial orientation. The body, head, and eyes were represented as three-dimensional coordinate frames, and the movement of these frames was related to a trajectory frame that described the motion of the body on a terrestrial plane. The axis-angle of the body, head, and eye rotation were then compared to the axis-angle of the rotation of the gravitoinertial acceleration (GIA). We inferred the role of the vestibular system during locomotion and the contributions of the VCR and VOR by examining the interrelationship between these coordinate frames. Straight walking induced head and eye rotations in a compensatory manner to the linear accelerations, maintaining head pointing and gaze along the direction of forward motion. Turning generated a combination of compensation and orientation responses. The head leads and steers the turn while the eyes compensate to maintain stable horizontal gaze in space. Saccades shift horizontal gaze as the turn is executed. The head pitches, as during straight walking. It also rolls so that the head tends to align with the orientation of the GIA. Head orientation changes anticipate orientation changes of the GIA. Eye orientation follows the changes in GIA orientation so that the net orientation gaze is closer to the orientation of the GIA. The study indicates that the vestibular system utilizes compensatory and orienting mechanisms to stabilize spatial orientation and gaze during walking and turning.

Eye Movements↗
PubMed2000

An analysis of orientation and ocular dominance patterns in the visual cortex of cats and ferrets.

We report an analysis of orientation and ocular dominance maps that were recorded optically from area 17 of cats and ferrets. Similar to a recent study performed in primates (Obermayer & Blasdel, 1997), we find that 80% (for cats and ferrets) of orientation singularities that are nearest neighbors have opposite sign and that the spatial distribution of singularities deviates from a random distribution of points, because the average distances between nearest neighbors are significantly larger than expected for a random distribution. Orientation maps of normally raised cats and ferrets show approximately the same typical wavelength; however, the density of singularities is higher in ferrets than in cats. Also, we find the well-known overrepresentation of cardinal versus oblique orientations in young ferrets (Chapman & Bonhoeffer, 1998; Coppola, White, Fitzpatrick, & Purves, 1998) but only a weak, not quite significant overrepresentation of cardinal orientations in cats, as has been reported previously (Bonhoeffer & Grinvald, 1993). Orientation and ocular dominance slabs in cats exhibit a tendency of being orthogonal to each other (Hubener, Shoham, Grinvald, & Bonhoeffer, 1997), albeit less pronounced, as has been reported for primates (Obermayer & Blasdel, 1993). In chronic recordings from single animals, a decrease of the singularity density and an increase of the ocular dominance wavelength with age but no change of the orientation wavelengths were found. Orientation maps are compared with two pattern models for orientation preference maps: bandpass-filtered white noise and the field analogy model. Bandpass-filtered white noise predicts sign correlations between orientation singularities, but the correlations are significantly stronger (87% opposite sign pairs) than what we have found in the data. Also, bandpass-filtered noise predicts a deviation of the spatial distribution of singularities from a random dot pattern. The field analogy model can account for the structure of certain local patches but not for the whole orientation map. Differences between the predictions of the field analogy model and experimental data are smaller than what has been reported for primates (Obermayer & Blasdel, 1997), which can be explained by the smaller size of the imaged areas in cats and ferrets.

Algorithms↗
PubMed2001

Visual response saturation to orientation contrast in the perception of texture boundary.

We analyzed how the visual response to orientation modulation in texture patterns varied as a function of the magnitude of orientation contrast. Using a contrast-discrimination technique, we measured threshold increments of orientation contrast (the orientation contrast required for discriminating between two textures) at various pedestal-orientation contrasts. The orientation-contrast-response function estimated for a step-orientation contrast, which produces a vivid percept of surface boundaries, saturated at approximately 30 degrees (experiment 1). The saturation was still evident even when the strength of the step-orientation contrast was reduced by orientation noise (experiment 2), but no strong saturation was found for textures that did not produce a vivid percept of surface boundaries (experiment 3). These results are consistent with the notion that orientation-based texture segregation involves the generation of a neural representation of the surface boundary whose strength is nearly independent of the magnitude of orientation contrast.

Contrast Sensitivity↗
PubMedDate not supplied

Health disparity in black women: lack of pharmaceutical advertising in black vs. white-oriented magazines.

CONTEXT: Racial disparities in health care between black women and white women may be attributed in part to socioeconomic status and lack of insurance, but also may be due to lack of the dissemination of health information in black communities via black popular magazines. OBJECTIVE: Comparison of the number and type of pharmaceutical advertisements between black-oriented magazines and white-oriented magazines. DESIGN: Descriptive study. SETTING: Morehouse School of Medicine. MAIN OUTCOME MEASURES: Recording of the type and number of over-the-counter and prescription drug advertisements. RESULTS: Five black-oriented magazines (Black Woman, Black Elegance, Essence, Ebony, and Upscale) and 5 white-oriented magazines (Family Circle, Working Mother, Good Housekeeping, Ladies' Home Journal, Women's Day) were evaluated for 3 months from June-August, 2000. White-oriented magazines had four to eight times more pharmaceutical ads than black-oriented magazines. Types of medications advertised in the white-oriented magazines and not the black-oriented magazines were, for example, cholinesterase inhibitors, calcium supplements, COX II-inhibitors, intranasal steroids, anorexiants, proton pump inhibitors, and smoking deterrent agents. Conversely, medications advertised in the black-oriented magazines and not the white-oriented magazines were antiviral agents and oral contraceptives. Pharmaceutical companies gave several reasons for the disparity, including the explanation that their particular company was advertising about HIV in the black community. CONCLUSIONS: A barrier to equitable health care for black women may be a low prioritization for health prevention and health management. This low prioritization or disinterest may be a reflection of the black magazine that she is reading due to the lack of pharmaceutical advertisements in black-oriented magazines. The result of this disinterest of black females may be seen in the increased morbidity and mortality for selected diseases.

Advertising↗
PubMed2002

Spatial constraints in bimanual coordination: influences of effector orientation.

Two experiments are reported that examined the influence of spatial orientation of the upper limbs in bimanual coordination. In both experiments, the upper limbs were oriented in either parallel, orthogonal, or obtuse spatial configurations and participants were asked to move their limbs continuously in temporal (1:1) synchrony, prepared in either in-phase or anti-phase modes of coordination. Bimanual coordination trials in Experiment 1 were paced by a metronome at one of four frequencies (1.0, 1.5, 2.0 or 2.5 Hz). Measures of relative phase accuracy and stability both revealed that, as metronome frequency increased, in-phase coordination dominated for the parallel spatial orientation, anti-phase coordination dominated for the orthogonal spatial orientation, and neither pattern dominated for the obtuse spatial orientations. In Experiment 2, an intentional switch method replicated and extended these influences of spatial orientation. The time to voluntarily switch from an anti-phase pattern to an in-phase pattern was faster than an in-phase to anti-phase switch (confirming support for the dominance of the in-phase pattern), but this was true only for the parallel spatial orientation. The reverse was true for the orthogonal spatial orientation (i.e., faster from in-phase to anti-phase), and no difference in switch times was observed for an obtuse spatial orientation. These findings support and extend previous research regarding the influence of spatial orientation in bimanual coordination and may be attributed to the role of, and potential interactions between, egocentric, allocentric, and mechanical constraints during action.

Adult↗
PubMed2005

Orientation selectivity in luminance and color vision assessed using 2-d band-pass filtered spatial noise.

We evaluated orientation discrimination in color and luminance vision using an external noise paradigm. Stimuli were spatiotemporal patches of 2D orientation noise isolating the achromatic, red-green and blue-yellow mechanisms, and matched in multiples of contrast detection threshold. We found a monotonic increase of orientation discrimination thresholds with the stimuli orientation bandwidths that is similar for both color and luminance contrasts. This dependence was fitted with two suitable models. A variance summation model suggests that internal orientation noise is significantly greater for the chromatic than for the achromatic mechanisms, while the efficiencies are similar. A gain control model of orientation tuning suggests that both chromatic and achromatic mechanisms are characterized by broadly tuned orientation detectors and that the relative chromatic deficit in orientation discrimination may only result from a slightly broader orientation tuning for the chromatic mechanisms. The moderate deficiency in chromatic orientation discrimination may account for the small differences found in shape perception between color and luminance vision.

Color Perception↗
PubMed2001

Orientation integration in detection and discrimination of contrast-modulated patterns.

Orientation detection and discrimination thresholds were measured for Gabor 'envelopes' formed from contrast-modulation of luminance 'carriers'. Consistent with previous research differences between carrier and envelope orientation had no effect on sensitivity to envelopes. Using plaid carriers in which the proportion of contrast modulation 'carried' by each plaid component was systematically manipulated, it was shown that this tolerance to carrier-envelope orientation difference reflects linear summation across orientation indicative of a single second-stage channel coding for contrast-defined structure. That contrast envelopes did not exhibit linear summation across spatial-frequency, nor across combinations of orientation and spatial-frequency differences, suggests that these second-order channels operate only within certain spatial scales. Using arrays of Gabor micropatterns as carriers in which the orientation distribution of the carriers was manipulated independently of the difference between envelope orientation and mean carrier orientation, it was further demonstrated that the locus of orientation integration must occur prior to envelope detection. In the context of two-stage models that incorporate a non-linearity between the stages, the pattern of results obtained is consistent with the operation of an orientation pooling process between first-stage and second-stage channels, analogous to having all filters of the first-stage feed into all filters of the second-stage within the same spatial-frequency band.

Contrast Sensitivity↗
PubMed1995

The McCollough effect reveals orientation discrimination in a case of cortical blindness.

BACKGROUND: The McCollough effect is a colour after-effect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns--such as a red-and-black vertical grating and a green-and-black horizontal grating--are viewed alternatively for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. RESULTS: Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90 degrees differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. CONCLUSIONS: These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.

Adult↗
PubMed1986

Decision processes in visual discrimination of line orientation.

The contribution of decision factors to the meridional variations in line orientation discrimination was determined for two-alternative forced-choice experimental designs. Using Johnson's (1980) formalization of decision processes in discrimination tasks, we identified three decision factors: the decision rule, memory variance, and criterial noise. In a first experiment, we showed the effect of experimental design on orientation discrimination to be similar at horizontal and oblique standard orientations, indicating that the meridional variations in orientation discrimination were not due to a decision rule anisotropy. In a second experiment, the effect of the interstimulus interval was also found to be similar at both standard orientations, suggesting that the memory variance is isotropic in the orientation domain. The results of two other experiments supported the hypothesis that the meridional variations in orientation discrimination are not due to a criterial noise anisotropy. These different results strongly suggested that the oblique effect in line orientation discrimination is due to sensorial factors rather than to decision factors. Therefore, they further support the hypothesis linking the anisotropy of the preferred orientation distribution of Area 17-S cells (a single physiologically defined class of cells in the primary visual cortex) and the meridional variations in line orientation discrimination.

Adult↗
PubMed2003

The spatial pattern of response magnitude and selectivity for orientation and direction in cat visual cortex.

Optical imaging studies of orientation and direction preference in visual cortex have typically used vector averaging to obtain angle and magnitude maps. This method has shown half-rotation orientation singularities (pinwheels) located within regions of low orientation vector magnitude. Direction preference is generally orthogonal to orientation preference, but often deviates from this, particularly in regions of low direction vector magnitude. Linear regions of rapid change in direction preference terminate in or near orientation singularities. The vector-averaging method is problematic however because it does not clearly disambiguate spatial variation in orientation tuning width from variation in height. It may also wrongly estimate preferred direction in regions where preference is weak. In this paper we analyze optical maps of cat visual cortex by fitting model tuning functions to the responses. This new method reveals features not previously evident. Orientation tuning height and width vary independently across the map: tuning height is always low near singularities, however regions of broad and narrow orientation tuning width can be found in regions of low tuning height, often alternating in a spoke-like fashion around singularities. Orientation and direction preference angles are always closely orthogonal. Reversals in direction preference form lines that originate precisely in orientation singularities.

Animals↗
PubMed2002

The manual haptic perception of orientations and the oblique effect in patients with left visuo-spatial neglect.

This study addresses the limits of haptic orientation deficit observed in patients with left visuo-spatial neglect (VSN) in the fronto-parallel plane. We concentrated on two aspects of the haptic perception of vertical, horizontal and oblique orientations: first, the global level of performances compared with normal subjects and, second, the occurrence of the oblique effect (i.e. lower performances in oblique orientations than in vertical-horizontal orientations). Subjects were asked to position a rod, presented in the fronto-parallel plane, to one of four orientations: vertical, horizontal, left 45 degrees oblique and right 45 degrees oblique. First, we found a haptic orientation deficit in neglect patients: The precision was lower in the neglect patients than in the normal (young adults and seniors) subjects. Second, we observed in both neglect patients and control subjects the occurrence of a similar haptic oblique effect and there were no differences between the results in the left and right hemispaces. Taken together, this means that, in spite of the global haptic orientation production deficit observed in VSN patients, no specific pattern was observed in the haptic production of different orientations in these subjects as compared to the two other groups. The haptic orientation deficit of neglect patients seems to affect in the same way all values and spatial positions of orientations.

Adult↗
PubMed2003

A spherical model for orientation and spatial-frequency tuning in a cortical hypercolumn.

A theory is presented of the way in which the hypercolumns in primary visual cortex (V1) are organized to detect important features of visual images, namely local orientation and spatial-frequency. Given the existence in V1 of dual maps for these features, both organized around orientation pinwheels, we constructed a model of a hypercolumn in which orientation and spatial-frequency preferences are represented by the two angular coordinates of a sphere. The two poles of this sphere are taken to correspond, respectively, to high and low spatial-frequency preferences. In Part I of the paper, we use mean-field methods to derive exact solutions for localized activity states on the sphere. We show how cortical amplification through recurrent interactions generates a sharply tuned, contrast-invariant population response to both local orientation and local spatial frequency, even in the case of a weakly biased input from the lateral geniculate nucleus (LGN). A major prediction of our model is that this response is non-separable with respect to the local orientation and spatial frequency of a stimulus. That is, orientation tuning is weaker around the pinwheels, and there is a shift in spatial-frequency tuning towards that of the closest pinwheel at non-optimal orientations. In Part II of the paper, we demonstrate that a simple feed-forward model of spatial-frequency preference, unlike that for orientation preference, does not generate a faithful representation when amplified by recurrent interactions in V1. We then introduce the idea that cortico-geniculate feedback modulates LGN activity to generate a faithful representation, thus providing a new functional interpretation of the role of this feedback pathway. Using linear filter theory, we show that if the feedback from a cortical cell is taken to be approximately equal to the reciprocal of the corresponding feed-forward receptive field (in the two-dimensional Fourier domain), then the mismatch between the feed-forward and cortical frequency representations is eliminated. We therefore predict that cortico-geniculate feedback connections innervate the LGN in a pattern determined by the orientation and spatial-frequency biases of feed-forward receptive fields. Finally, we show how recurrent cortical interactions can generate cross-orientation suppression.

Brain Mapping↗
PubMed1978

Physiological consequences for the cat's visual cortex of effectively restricting early visual experience with oriented contours.

1. The early visual experience of nine cats was restricted to viewing horizontal or vertical lines inside opaque goggles. 2. When the kittens were 3-4 mo old, extracellular recordings were made in the primary visual cortex. To obtain a representative sample of cortical cells, units were studied at regularly spaced intervals along the course of electrode penetrations traveling oblique to the cortical surface. An automated assessment of preferred orientation using a computer-driven optical display was employed, and during the recording session the experimenters did not know which orientation(s) each animal had viewed in early life. 3. In the cats that viewed horizontal lines with one eye and vertical lines with the other during rearing, two major findings of previous workers (14) were confirmed. First, a majority of units were not selective for orientation. Second, units with preferred orientations near vertical tended to be activated exclusively by the eye that had viewed vertical, and likewise for horizontal. 4. In cats that viewed lines of the same orientation with both eyes during rearing, a substantially smaller proportion of units were selective for orientation; the preferred orientations of these units also tended to match the orientation to which the cats had been exposed. 5. Portions of some electrode penetrations showed an orderly arrangement of cells according to preferred orientation similar to that seen in normal cats, but with regions over which only nonselective cells were found. Many penetrations appeared less orderly. 6. The results are consistent with a role for early visual experience in maintaining the responsiveness and innate selectivity of cortical neurons, although they cannot entirely rule out the possibility that experience may alter or determine the preferred orientation of some cells.

Animals↗
PubMed1994

Activity of inferior temporal neurons during orientation discrimination with successively presented gratings.

1. We recorded from inferior temporal (IT) cells in three monkeys while they performed an orientation discrimination task with successively presented gratings. Histological reconstruction of two monkey brains indicated that most recordings were from TE3. The task was exactly the same as the one used in a previous V1 study, allowing direct comparison. 2. One quarter of IT cells were responsive to the grating. Response strength and variability of the cells excited by the grating (n = 341) were similar to those in V1, whereas response latency was on average 40 ms longer than in V1. 3. In one third of the responsive cells orientation had a significant effect. Sensitivity for orientation was captured by the orientation sensitivity index, which ranged from 0 to 0.95 with a median of 0.23. Orientation sensitivity of IT cells was on average much less than that of V1 cells. More cells preferred horizontal and vertical than oblique orientations. 4. The differences in responsiveness and orientation sensitivity among individual animals could be accounted for by the anterior/posterior difference in recording position. 5. Task-related behavioral effects were examined in 283 cells that were responsive to the visual stimuli. Order effects were examined in "same" trials and occurred in half of the IT cells in each of the three monkeys. In these cells there was on average a threefold difference in response between the first stimulus (S1) and the second stimulus in same trials (S2same). In two monkeys the average response to S2same was less than that to S1, whereas in the third monkey the average response to S1 was smaller than that to S2same. 6. IT cells also exhibited same/different effects, whereby response to a physically identical second stimulus differed between same and "different" trials. Generally cells responded more to the second stimulus in different trials than to S2same but the opposite also occurred. For a subset of these cells we could show that the correct/error type of the trial had no effect and that the response occurred before the saccadic response. 7. These context effects were modulations of the gain of the orientation tuning curves for the different types of responses. The tuning for orientation of these different responses was similar. 8. One third of the responsive IT cells exhibited an increased activity in the interstimulus interval (ISI), fitting the definition of delay cells. This activity was maintained when the ISI was lengthened from 300 to 800 ms. The orientation tuning of this response was similar to that for S1 responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Reaching movements with similar hand paths but different arm orientations. I. Activity of individual cells in motor cortex.

This study shows that the discharge of many motor cortical cells is strongly influenced by attributes of movement related to the geometry and mechanics of the arm and not only by spatial attributes of the hand trajectory. The activity of 619 directionally tuned cells was recorded from the motor cortex of two monkeys during reaching movements with the use of similar hand paths but two different arm orientations, in the natural parasagittal plane and abducted into the horizontal plane. Nearly all cells (588 of 619, 95%) showed statistically significant changes in activity between the two arm orientations [analysis of variance (ANOVA). P < 0.01]. A majority of cells showed a significant change in their overall level of activity (ANOVA, main effect of task, P < 0.01) between arm orientations before, during, and after movement. Many cells (433 of 619, 70%) also showed a significant change in the relation of their discharge with movement direction (ANOVA, task x direction interaction term, P < 0.01) during movement, including changes in the dynamic range of discharge with movement and changes in the directional preference of cells that were directionally tuned in both arm orientations. Similar effects were seen for the discharge of cells while the monkey maintained constant arm postures over the different peripheral targets with the use of different arm orientations. Repeated data files from the same cell with the use of the same arm orientation showed only small changes in the level of discharge or in directional tuning, suggesting that changes in cell discharge between arm orientations cannot be explained by random temporal variations in cell activity. The distribution of movement-related preferred directions of the whole sample differed between arm orientations, and also differed strongly between cells receiving passive input predominantly from the shoulder or elbow. The electromyographic activity of most prime mover muscles at the shoulder and elbow was also strongly affected by arm orientation, resulting in changes in overall level of activity and/or directional tuning that often resembled those of the proximal arm-related motor cortical cells. A mathematical model that represented movements in terms of movement direction centered on the hand could not account for any of the arm-orientation-related response changes seen in this task, whereas models in intrinsic parameter spaces of joint kinematics and joint torques predicted many of the effects.

Analysis of Variance↗
PubMed2000

Contextual influence on orientation discrimination of humans and responses of neurons in V1 of alert monkeys.

We studied the effects of various patterns as contextual stimuli on human orientation discrimination, and on responses of neurons in V1 of alert monkeys. When a target line is presented along with various contextual stimuli (masks), human orientation discrimination is impaired. For most V1 neurons, responses elicited by a line in the receptive field (RF) center are suppressed by these contextual patterns. Orientation discrimination thresholds of human observers are elevated slightly when the target line is surrounded by orthogonal lines. For randomly oriented lines, thresholds are elevated further and even more so for lines parallel to the target. Correspondingly, responses of most V1 neurons to a line are suppressed. Although contextual lines inhibit the amplitude of orientation tuning functions of most V1 neurons, they do not systematically alter the tuning width. Elevation of human orientation discrimination thresholds decreases with increasing curvature of masking lines, so does the inhibition of V1 neuronal responses. A mask made of straight lines yields the strongest interference with human orientation discrimination and produces the strongest suppression of neuronal responses. Elevation of human orientation discrimination thresholds is highest when a mask covers only the immediate vicinity of the target line. Increasing the masking area results in less interference. On the contrary, suppression of neuronal responses in V1 increases with increasing mask size. Our data imply that contextual interference observed in human orientation discrimination is in part directly related to contextual inhibition of neuronal activity in V1. However, the finding that interference with orientation discrimination is weaker for larger masks suggests a figure-ground segregation process that is not located in V1.

Action Potentials↗
PubMed2000

Conjunctions of colour, luminance and orientation: the role of colour and luminance contrast on saliency and proximity grouping in texture segregation.

To examine whether perceptual grouping on the basis of orientation can be performed simultaneously with or only subsequently to grouping according to colour or luminance, we tested whether subjects are able to segregate arrays of texture elements that differ from surrounding elements by conjunctions of either (i) colour and orientation, or (ii) luminance contrast and orientation, or (iii) luminance contrast polarity and orientation. Subjects were able to use conjunctions between luminance and orientation for segregation but not conjunctions between colour or contrast polarity and orientation. Our results suggest that (i) in agreement with earlier findings, there seem to exist no specific conjunction detectors for colour and orientation or contrast polarity and orientation, and (ii) when orientation defined textures are to be distinguished by virtue of differences in luminance, colour, or contrast polarity, luminance provides a much stronger cue than colour or contrast polarity for saliency-based orientation grouping.

Adaptation, Ocular↗
PubMed2002

Energy and phase orientation mechanisms: a computational model.

A computational model is proposed for spatial orientation processing beyond the initial stage of linear filtering in visual cortex. The model accounts for orientation pop-out, edge location and orientation, and bar location and orientation. It naturally extends to higher order orientation symmetries. The model is consistent with much of the current understanding of early processing in mammalian visual cortex. It builds on the notions of orientation and spatial frequency specific simple cells, any subsequent non-linearity, and orientation 'pooling'. The processing treats simple cell energy, real, and imaginary responses in a unified way to generate 'feature maps'. The 'pooling' operation in each case is a discrete Fourier transform of the simple cell responses over orientation. The suggested processing has implications for psychophysics (e.g. providing an explanation of why orientation discrimination thresholds are more than an order of magnitude less than simple cell orientation bandwidths), provides some understanding of the variety of 'complex-cell' properties found in visual cortex, and provides a plausible starting point for subsequent processing.

Computer Simulation↗