Orientation-sensitive Neurons Research Articles

Single-layer perceptron artificial visual system for orientation detection.

Orientation detection is an essential function of the visual system. In our previous works, we have proposed a new orientation detection mechanism based on local orientation-selective neurons. We assume that there are neurons solely responsible for orientation detection, with each neuron dedicated to detecting a specific local orientation. The global orientation is inferred from the local orientation information. Based on this mechanism, we propose an artificial visual system (AVS) by utilizing a single-layer of McCulloch-Pitts neurons to realize these local orientation-sensitive neurons and a layer of sum pooling to realize global orientation detection neurons. We demonstrate that such a single-layer perceptron artificial visual system (AVS) is capable of detecting global orientation by identifying the orientation with the largest number of activated orientation-selective neurons as the global orientation. To evaluate the effectiveness of this single-layer perceptron AVS, we perform computer simulations. The results show that the AVS works perfectly for global orientation detection, aligning with the majority of physiological experiments and models. Moreover, we compare the performance of the single-layer perceptron AVS with that of a traditional convolutional neural network (CNN) on orientation detection tasks. We find that the single-layer perceptron AVS outperforms CNN in various aspects, including identification accuracy, noise resistance, computational and learning cost, hardware implementation feasibility, and biological plausibility.

Titchener's T in context 2 – Symmetric patterns of two Ts

Patterns of two Ts, materializing different symmetry groups, were used to explore conditions that would lead to a modulation of the typically observed overestimation of the length of a T's undivided line relative to its divided line. Observers either had to compare the lengths of the lines of one or the other of the Ts in a pattern, or noncorresponding lines between the two Ts. For both tasks alike, the T-illusion was found to be markedly greater with twofold mirror-symmetric 2-T patterns than it usually is with individual Ts. A control experiment suggested that the effect was probably due to the collinearity of the two Ts' undivided lines in these patterns rather than the additional axis of mirror symmetry. Findings are interpreted in terms of interactions between orientation-sensitive neurons that respond to the Ts' individual lines.

A Survey of Architecture and Function of the Primary Visual Cortex (V1)

The largest visual area, known as the primary visual cortex or V1, has greatly contributed to the current understanding of mammalian and human visual pathways and their role in visual perception. The initial discovery of orientation-sensitive neurons in V1, arranged according to a retinotopic mapping, suggested an analogy to its function as a low-level feature analyser. Subsequent discoveries of phase, spatial frequency, color, ocular origin, and direction-of-motion-sensitive neurons, arranged into overlapping maps, further lent support to the view that it performs a rich decomposition, similar to signal processing transforms, of the retinal output. Like the other cortical areas, V1 has a laminar organization with specialization for input from the relayed retinal afferents, output to the higher visual areas, and the segregation of the magno (motion) and parvo (form) pathways. Spatially lateral connections that exist between neurons of similar and varying properties have also been proposed to give rise to a computation of a bottom-up saliency map in V1. We provide a review of the selectivity of neurons in V1, laminar specialization and analogies to signal processing techniques, a model of V1 saliency computation, and higher-area feedback that may mediate perception.

Slab-like functional architecture of higher order cortical area 21a showing oblique effect of orientation preference in the cat

Optical imaging based on intrinsic signals is a powerful tool for in vivo studying functional organization of various cortices. Here, the functional architecture of orientation-sensitive neurons in higher order extrastriate cortical area 21a was investigated in cats using optical imaging combined with electrophysiological methods. It is found that neurons in area 21 with similar preferred orientations were functionally organized into a slab-like columnar structure orthogonal to the cortical surface, and the orientation columns were distributed more densely than those in area 17. The responsiveness and activated areas of optical maps visually elicited by the horizontal and vertical gratings were always larger than those by oblique gratings in areas 21a and 17. This neural oblique effect shown in orientation maps was more significant in area 21a than that in area 17. The findings suggest a neuronal mechanism in the higher order extrastriate cortex involving the visual perceptive process of the superiority of cardinal contours.

Limiting factors for the detection of orientation.

First steps of visual-information processing in primates are characterised by a highly ordered representation of the outside world on the cortex. Two prominent features of cortical organisation are the retinotopic mapping of position in the visual field on the first stages of the visual stream, and the systematic variation of orientation preference in the same areas. In an attempt to understand the relation of position and orientation representation, we need to know the minimum spatial requirements for orientation detection. In the present paper, the spatial limits for detecting orientation are analysed by simulating simple orientation filters and testing the ability of human observers to detect the orientation of small lines at various positions in the visual field. At sufficiently high contrast levels, the minimum physical length of a line to discriminate orientation differences of 45 degrees-90 degrees is not constant when presented at various eccentricities, but covaries inversely with the cortical magnification factor. In consequence, a line needs to correspond to about 0.2 mm of cortical surface, independently of the actual eccentricity at which the stimulus is presented, in order to allow observers to recognise its orientation. This has consequences for our understanding of orientation detection. (i) In combination with simulation experiments, it becomes clear that the elementary process underlying orientation detection is a local operation, which seems to focus on small regions compared with cortical receptive fields. (ii) With respect to the number of inputs to the visual cortex, the performance of this local operation approaches the physical limits, requiring hardly more than three-four input LGN axons to be activated for detecting the orientation of a highly visible line segment. Comparing these spatial characteristics with the receptive fields of orientation-sensitive neurons in the primate visual system could suggest new insights into the neuronal circuits underlying orientation mapping in the human cortex.

The Detection of Orientation of Small Objects

Visual information processing in primate cortex is based on a highly ordered representation of the surrounding world. In addition to the retinotopic mapping of the visual field, systematic variations of the orientation tuning of neurons are described electrophysiologically for the first stages of the visual stream. On the way to understanding the relation of position and orientation representation, in order to give an adequate account of cortical architecture, it will be an essential step to define the minimum spatial requirements for detection of orientation. We addressed the basic question of spatial limits for detecting orientation by comparing computer simulations of simple orientation filters with psychophysical experiments in which the orientation of small lines had to be detected at various positions in the visual field. At sufficiently high contrast levels, the minimum physical length of a line whose orientation can just be resolved is not constant when presented at various eccentricities, but covaries inversely with the cortical magnification factor. A line needs to span less than 0.2 mm on the cortical surface in order to be recognised as oriented, independently of the actual eccentricity at which the stimulus is presented. This seems to indicate that human performance for this task approaches the physical limits, requiring hardly more than approximately three input elements to be activated, in order to detect the orientation of a highly visible line segment. Combined with the estimates for receptive field sizes of orientation-selective filters derived from computer simulations, this experimental result may nourish speculations of how the rather local elementary process underlying orientation detection in the human visual system can be assembled to form much larger receptive fields of the orientation-sensitive neurons known to exist in the primate visual system.

Neural Mechanisms in Boundary Grouping, Illusory Contour Generation, and Spatial Tuning of Receptive Field Selectivity

A model for cortical boundary detection and contour grouping at visual cortical areas V1 and V2 is presented. The functional organisation of the model architecture is based on principles of adaptive resonance theory (Grossberg, 1980 Psychological Review87 1 – 51). The primary visual areas are connected in a bidirectional scheme of feedforward and feedback projections. Signal features are initially measured by orientation-sensitive neurons at the simple and complex cell level. These measurements undergo local competitive processing and subsequent nonlinear bipole integration of coherent activity (von der Heydt and Peterhans, 1988 Journal of Neuroscience9 1731 – 1748). The integration is based on an antagonistic interaction in position and orientation space utilising spatial coupling and compatibility functions for the evaluation of coherent activity distributions. This step can therefore be interpreted as implementing a process of matching neural codes of most-likely contour outlines against the noisy input distribution of local contrast measurements. The result of the integration stage is fed back to the first competitive stages to enhance compatible activations via multiplicative gating. The net effect produces grouping and illusory contour completion. In particular, the results of model simulations demonstrate that (i) the orientation selectivity of V1 cells is sharpened depending on the spatial arrangement and visual context, (ii) orientation-selective contrast measurements are enhanced at boundaries of spatially homogeneous stimulus arrangements and suppressed in the interiors, (iii) oriented cells at model V2 stage only respond to curvilinear input arrangements of activity at both branches of bipole cells, and (iv) model V2 cells show fine tuning for orientation selectivity and generate subjective contours to bridge gaps in arrangements of oriented contrast.

Use of segment arrays to evaluate the strength of angular induction

The contribution of local and global influence on angular induction was evaluated by varying the orientation of individual segments that were organized into an array. It was found that some of the misprojection of an oblique is determined by the orientation of the individual segments, and some by the overall configuration of the segments into two parallel bands. These results are integrated into a model that views angular induction as a lateral bias among orientation-sensitive neurons, with global influence differing from local influence only as a matter of scale.

Coding of the spatial period of gratings rolled across the receptive fields of somatosensory cortical neurons in awake monkeys.

In order to measure the texture coding capabilities of motion-, direction-, and orientation-sensitive neurons in SI cortex, we rolled wheels with surface milled gratings across their receptive fields. Gratings of spatial periods 0.8-9.6 mm were presented in pseudorandom order; each was tested 5-20 times in the distal, proximal, radial, and ulnar directions. Thirty eight cortical neurons were studied with three to eight different gratings in order to determine the effect of spatial period on neuronal firing rates. While all 38 cells had their firing rates modulated by motion of the gratings, only 11 neurons were able to distinguish changes in its spatial period. These cells had small receptive fields located on the hand. Most motion-sensitive neurons showed little effect of spatial period on firing rates and had relatively flat frequency response curves. One showed decreased firing to spatial periods over the range 0.8-6.4 mm; three others increased their firing rates over the range 0.8-3.2 mm, followed by a decline in activity to larger spatial periods. Direction- and orientation-sensitive neurons showed only minor changes in firing rates as a function of spatial period. Sixteen cells showed flat frequency response functions, three showed increased firing rates, and four decreased firing rates as spatial period of the grating increased. Direction and orientation preferences were maintained over the range 0.8-9.6 mm for all 23 neurons tested. Although four cells showed a drop in direction index (DI) as the spatial period was increased, none showed a loss of direction sensitivity, as DI was greater than 35 for all gratings tested. Two neurons showed increased firing to motion in the last-preferred direction and two others decreased firing in the best direction. The remaining 19 neurons showed parallel effects of texture in all directions. Some motion-sensitive neurons showed weak direction preferences when tested with fine gratings; these preferences disappeared with coarser gratings, due to increased responsiveness to motion in the least-preferred direction. These data demonstrate that movement-sensitive neurons do not require continuous trajectories across the skin but instead sequential activation of points aligned in a specific path. Cortical neurons appear capable of integrating information from points separated by up to 9 mm, as long as they are presented in the appropriate temporal sequence. Firing rates of direction- and orientation-sensitive neurons are more profoundly modified by changes in the direction of motion across the skin, and the temporal order of stimulation, than by alterations in the spatial characteristics of the moving stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Head orientation and meridional variations in acuity

Contrast sensitivity was measured for sinusoidal gratings in different retinal orientations. Oblique gratings of high spatial-frequency are less resolvable than vertical ones. This confirms earlier results and is attributed to properties of orientation-sensitive cortical neurons. The advantage of retinally vertical over oblique gratings persists when the head is tilted and does not change during the next half hour. It is concluded that the properties of orientation-sensitive neurons are not significantly altered in the short term.