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PubMed2005

Whisker-based discrimination of object orientation determined with a rapid training paradigm.

Rats use their large facial whiskers to discriminate the spatial features of objects. Despite numerous electrophysiological recording studies in the central trigeminal whisker representations that document neurons tuned to the direction of whisker deflection, there is no behavioral evidence to date that rats can use their whiskers to discriminate between object orientations. In the present study, we characterized whisker-dependent orientation discrimination using a one-trial learning procedure. Sprague-Dawley rats were trained and tested in a three-arm 'Y-maze' that was outfitted with 180 independently moveable bars that protruded into the arms of the maze to contact the whiskers. On the first day, the maze was configured to have two arms with only horizontal bars and a third arm with only vertical bars and rats were allowed to freely explore all arms. On the second day, rats were isolated in one arm that contained only vertical bars as a conditioned stimulus (CS) and administered three mild foot shocks. On the third day, the maze was configured identically to the first day and rats were once again allowed to freely explore the maze. We measured the percentage of time spent in each arm of the maze and found that most rats spent significantly less time in the arm containing the CS after training compared to before training. Subsequent control experiments determined that the conditioned avoidance was attributable to orientation cues, was caused by the association of the conditioned and unconditioned stimulus and was whisker-dependent. Avoidance behavior was significantly reduced when the difference between the conditioned and non-conditioned orientation difference was reduced to 45 degrees. Thus, rats can discriminate object orientation with their whiskers and an estimate of their discrimination thresholds can be rapidly acquired through the application of a one-trial learning paradigm.

Afferent Pathways↗
PubMed2004

Effects of contrast and size on orientation discrimination.

Motivated by the recent physiological finding that a neuron's receptive field can increase in size by a factor of 2-4-fold at low contrast [Nat. Neurosci. 2 (1999) 733, Proc. Natl. Acad. Sci. USA 96 (1999) 12073], we sought to examine whether a psychophysical task might reflect the contrast dependent changes in the size/structure of a receptive field. We postulate that since spatial summation is not contrast invariant, a task that relies on the spatial structure of a receptive field, such as orientation discrimination, should also be affected by changes in contrast. Previously, orientation discrimination thresholds have been reported to be roughly independent of the contrast of a stimulus for most of the visible range of contrasts [i.e. J. Neurophysiol. 57 (1987) 773, J. Opt. Soc. Am. 6 (1989) 713, Vis. Res. 30 (1990) 449, Vis. Res. 39 (1999) 1631]. Here, we found large improvements in orientation discrimination with contrast that were dependent on stimulus area. Furthermore, the apparent constancy of orientation discrimination for large area stimuli is possibly a result of a floor effect on the threshold. Therefore we conclude that there is not strong evidence for contrast invariant orientation discrimination. We interpret these results in the context of recent neurophysiological results about the expansion of cortical cells' receptive fields at low contrast.

Contrast Sensitivity↗
PubMed2004

Combining cues in contour orientation discrimination.

The perceived orientation of a Gabor-patch contour is determined, in part, by shifts in carrier phase between the patches [Popple, A. V. & Sagi, D., 2000. A Fraser illusion without local cues? Vision Research, 40, 873-878; Popple, A. V. & Levi, D. M., 2000a. A new illusion demonstrates long-range processing. Vision Research, 40, 2545-2549; Popple, A. V. & Levi, D. M., 2000b. Amblyopes see true alignment where normal observers see illusory tilt. Proceedings of the National Academy of Sciences of the United States of America, 97, 11667-11672]. Here we show that perceived orientation results from the combination of at least three stimulus cues: (1) patch orientation, (2) contour envelope orientation, and (3) between-patches orientation, which is a function of phase-shifts. In a series of three experiments, we investigated how these three cues were combined. The data are consistent with weighted cue combination.

Bayes Theorem↗
PubMed2004

Is there opponent-orientation coding in the second-order channels of pattern vision?

Is there opponency between orientation-selective processes in pattern perception, analogous to opponency between color mechanisms? Here we concentrate on possible opponency in second-order channels. We compare several possible second-order structures: SIGN-opponent-only channels in which there is no opponency between orientations (also called complex channels or filter-rectify-filter mechanisms); three structures we group under the name ORIENTATION-opponent; and finally BOTH-opponent channels which combine features of both SIGN-opponent-only and ORIENTATION-opponent channels but lead to predictions that are distinct from either of theirs. We measured observers' ability to segregate textures composed of checkerboard and striped arrangements of vertical and horizontal Gabor grating patches. The observers' performance was compared to model predictions from the alternative opponent structures. The experimental results are consistent with SIGN-opponent-only channels. The results rule out the ORIENTATION-opponent and BOTH-opponent structures. Further, when the models were expanded to include a contrast gain-control (inhibition among channels in a normalization network) the SIGN-opponent-only model was also able to explain a contrast-dependent effect we found, thus providing another piece of evidence that such normalization is an important process in human texture perception.

Adult↗
PubMed2005

Motion- and orientation-specific cortical responses in infancy.

During the first 3 months, infants develop visual evoked potential (VEP) responses that are signatures of cortical orientation-selectivity and directional motion selectivity. Orientation-specific cortical responses develop in early infancy. This study compared these responses directly in the same infants, to investigate whether the later appearance of direction selectivity was intrinsic, or a function of the spatio-temporal characteristics of the stimuli used. Steady-state orientation-reversal (OR-) VEPs and direction-reversal (DR-) VEPs were recorded in infants aged 4-18 weeks. DR-VEPs were elicited with random pixel patterns and with gratings spatially similar to those used for OR-VEPs, at velocities of 5.5 and 11 deg/s, and reversal rates of 2 and 4 reversals/s. Infants throughout the age range showed significant responses to orientation-reversal. Direction-reversal responses appeared in less than 25% of infants under 7 weeks of age, rising to 80% or more at 11-13 weeks, whether tested with dots or gratings and for both speeds and reversal rates. However, 2 reversals/s elicits the DR-VEP on average about 2 weeks earlier than 4 reversal/s stimulation. We conclude that human cortical direction selectivity develops separately from orientation-selectivity and emerges at a later age, even with tests that are designed to optimise the former.

Aging↗
PubMed2006

Surface orientation, modulation frequency and the detection and perception of depth defined by binocular disparity and motion parallax.

Binocular disparity and motion parallax provide information about the spatial structure and layout of the world. Descriptive similarities between the two cues have often been noted which have been taken as evidence of a close relationship between them. Here, we report two experiments which investigate the effect of surface orientation and modulation frequency on (i) a threshold detection task and (ii) a supra-threshold depth-matching task using sinusoidally corrugated surfaces defined by binocular disparity or motion parallax. For low frequency corrugations, an orientation anisotropy was observed in both domains, with sensitivity decreasing as surface orientation was varied from horizontal to vertical. In the depth-matching task, for surfaces defined by binocular disparity the greatest depth was seen for oblique orientations. For surfaces defined by motion parallax, perceived depth was found to increase as surface orientation was varied from horizontal to vertical. In neither case was perceived depth for supra-threshold surfaces related to threshold performance in any simple manner. These results reveal clear differences between the perception of depth from binocular disparity or motion parallax, and between perception at threshold and supra-threshold levels of performance.

Cues↗
PubMed2006

Sensitivity and configuration-specificity of orientation-defined texture processing in infants and adults.

Here we use textures made up of widely spaced Gabor patches to compare infant and adult sensitivity to the global organization of the elements comprising the textures. Visual Evoked Potentials (VEPs) were recorded to alterations between random images and images containing varying proportions of patches that were of the same orientation. The patches were placed on rectangular, hexagonal or random lattices. Texture-specific responses were robust in adults and their VEP threshold was reached when 1-17% of the patches had the same orientation in the structured image. Infant thresholds were approximately 20-60%. While infants are capable of detecting the global structure of our textures, their sensitivity is low. In adults we found, unexpectedly, that sensitivity and response gain were higher for horizontal compared to vertical global orientations. Infant sensitivity was the same for the two orientations. Comparable orientation anisotropies have not been previously reported for gratings, suggesting that the Gabor-defined textures are tapping different mechanisms. There were small, but measurable effects of the lattice type in adults, with the rectangular lattice producing the largest responses.

Adult↗
PubMed2000

Summation of texture segregation across orientation and spatial frequency: electrophysiological and psychophysical findings.

Objects are usually segregated from ground by several visual dimensions. We studied texture segregation in checkerboards defined by gradients in spatial frequency, orientation or both frequency and orientation, using Gabor-filtered noise patterns. Saliency was measured electrophysiologically using the visual evoked potential (VEP) associated with texture segregation ('tsVEP') (an associated component in the visual evoked potential), and psychophysically by a 2AFC task. Spatial frequency and orientation stimuli evoked percepts of texture segregation and tsVEPs in all 11 subjects. The tsVEPs to combined stimuli were larger than those to each dimension alone, but smaller (74%) than the algebraic sum of tsVEPs to both individual dimensions. Psychophysical detection rates differed significantly between all conditions (P < 0.001), with highest rates for the combined stimuli. The findings suggest that segregation based on a combination of 'orientation' and 'spatial frequency' is more salient than that based on either of these alone. The significant deviation from full additivity in the tsVEPs suggests that simultaneous contrasts in spatial frequency and orientation have a common processing stage.

Evoked Potentials, Visual↗
PubMed2001

Orientation processing mechanisms revealed by the plaid tilt illusion.

The tilt after-effect (TAE) and tilt illusion (TI) have revealed a great deal about the nature of orientation coding of 1-dimensional (1D) lines and gratings. Comparatively little research however has addressed the mechanisms responsible for encoding the orientation of 2-dimensional (2D) plaid stimuli. A multi-stage model of edge detection has recently been proposed [Georgeson, M. A. (1998) Image & Vision Computing, 16(6-7), 389-405] to account for the perceived structure of a plaid stimulus that incorporates extraction of the zero-crossings (ZCs) of the plaid. Data is presented showing that the ZCs of a plaid inducing stimulus can interact with vertical grating test stimulus to induce a standard tilt illusion. However, by considering the second-order structure of a plaid rather than ZCs, it was shown that the perceived orientation of the vertical test grating results from the combination of orientation illusions due to the first- and second-order components of an inducing plaid. The data suggest that the mechanisms encoding the orientation of second-order contours are similar to, and interact directly with, those that encode first-order contours.

Contrast Sensitivity↗
PubMed2003

Orientation discrimination in visual noise using global and local stimuli.

We have investigated orientation discrimination in visual noise using two types of high contrast, broadband stimuli. Discrimination thresholds are better for Local stimuli, in which the orientation signal is spatially limited, than for Global stimuli, in which the orientation signal extends across the entire stimulus. Performance improves with increasing stimulus area, reaching an optimum threshold of about 11% orientation signal. Thresholds were not influenced by brief presentation times or practice. These results, along with results from a simple computational model, suggest that human orientation discrimination for this kind of pattern is mediated by pooling local responses of low-level neural mechanisms and is limited by two stages of intrinsic neural noise.

Discrimination, Psychological↗
PubMed2006

Sound as an orientation cue for the pelagic larvae of reef fishes and decapod crustaceans.

The pelagic life history phase of reef fishes and decapod crustaceans is complex, and the evolutionary drivers and ecological consequences of this life history strategy remain largely speculative. There is no doubt, however, that this life history phase is very significant in the demographics of reef populations. Here, we initially discuss the ecology and evolution of the pelagic life histories as a context to our review of the role of acoustics in the latter part of the pelagic phase as the larvae transit back onto a reef. Evidence is reviewed showing that larvae are actively involved in this transition. They are capable swimmers and can locate reefs from hundreds of metres if not kilometres away. Evidence also shows that sound is available as an orientation cue, and that fishes and crustaceans hear sound and orient to sound in a manner that is consistent with their use of sound to guide settlement onto reefs. Comparing particle motion sound strengths in the field (8 x 10(-11) m at 5 km from a reef) with the measured behavioural and electrophysiological threshold of fishes of (3 x 10(-11) m and 10 x 10(-11), respectively) provides evidence that sound may be a useful orientation cue at a range of kilometres rather than hundreds of metres. These threshold levels are for adult fishes and we conclude that better data are needed for larval fishes and crustaceans at the time of settlement. Measurements of field strengths in the region of reefs and threshold levels are suitable for showing that sound could be used; however, field experiments are the only effective tool to demonstrate the actual use of underwater sound for orientation purposes. A diverse series of field experiments including light-trap catches enhanced by replayed reef sound, in situ observations of behaviour and sound-enhanced settlement rate on patch reefs collectively provide a compelling case that sound is used as an orientation and settlement cue for these late larval stages.

Animals↗
PubMed1996

Firing characteristics of neurones in the superior colliculus and the pontomedullary reticular formation during orienting in unrestrained cats.

Cats were trained to fixate a center LED or light spot for 1-10 s and to orient to a target (LED or light spot), which appeared simultaneous with the disappearance of the fixation light. Firing characteristics of neurones in the superior colliculus (SC) and the pontomedullary reticular formation were examined systematically in cats performing the above orienting task. In the head-free condition, a majority of the superficial neurones in the SC was activated when a target appeared in a particular area in the visual field (receptive field) as in head fixed animals. We identified a new group of neurones in superficial layers of the SC, superficial fixation neurones, which fired tonically when fixated on a target light with little activity at fixating a center fixation light. In the intermediate and deep layers of the SC, many neurones fired when directed to a particular area in the visual field (movement field). In addition to these neurones, we found new groups of neurones fired tonically in a particular phase of orienting. These neurones were divided into three principal types, target activated, target suppressed and center fixation activated neurones. Target activated neurones fired tonically during the fixation of a target, but not during fixation of a center spot. Target suppressed neurones were characterized by a pause during fixation of targets irrespective of their location. They had clear phasic and tonic components. The phasic component was characterized by a movement field resembling that seen in a typical intermediate layer neurone. Center fixation activated neurones discharged during fixation of the center spot and exhibited suppression during fixation of the target. Many neurones in the pontomedullary reticular formation fired during orienting. Four major types of neurones, phasic, phasic sustained, pause and tonic neurones, were differentiated on the basis of their firing patterns. Phasic units were characterized by brief phasic firing during orienting and could be divided into four subtypes. Long lead phasic neurones began to fire 50-100 ms prior to the onset of a gaze shift and stopped well before the end of the gaze shift and the total number of firing was best correlated with the total angle of head rotation. Short lead phasic neurones started to fire 10-20 ms prior to a gaze shift and were further subdivided into decrement and plateau types. The decrement type exhibited a brief burst just prior to gaze shift and stopped discharging prior to the end of the gaze shift, while the plateau type fired tonically during the gaze shift and stopped firing after the gaze shift. Total number of discharges of both type was related to maximal angular velocity. The fourth type, gaze neurone, began firing coincident with the onset of the gaze shift and stopped firing at the completion of the gaze shift and the total number of discharges was closely related to total angle of head rotation Phasic sustained (PS) neurones fired 50-100 ms before the onset of a gaze shift and their discharges continued after the end of the gaze shift and were divided into three subtypes: augmenting, pause and plateau. The augmenting type was characterized by a transient increase of firing during the gaze shift and a maintained slow rate of firing following the gaze shift. Total number of discharges related to head movement amplitude and the sustained activity was correlated with head position. The pause type was suppressed during the gaze shift and was tonically active during a head movement. The plateau type had a weak phasic component and discharged at a fairly constant rate. The pause and plateau types appeared to be related to head amplitude and head position, respectively. Tonic units were classified into several types. Target fixation neurones exhibited sustained firing when the cat was fixating a target, irrespective of its location, but did not show sustained firing when the animal fixated the fixation light. Fixation neurones fired tonical

Animals↗
PubMed2002

Effects of monocular viewing on orientation in an arena at the release site and homing performance in pigeons.

Orientation and homing performance of pigeons with the left or right eye occluded were assessed in an arena at the release site and during the subsequent homing flight. Three release sites near Pisa, Italy, were used. Compared to binocular controls, monocular birds showed a bias in orientation towards the side of the viewing eye. In the arena, this bias was considerable and the mean deviation corresponded to the angle of the optical axis, suggesting a systematic error in visual representation during directional orientation. During flight after leaving the arena the directional bias decreased and the homeward orientation increased. While there was a slight lateralization of overall homing performance in favour of the right eye, there was no lateralization in directional orientation in the arena or at vanishing. Our results show that navigational mechanisms in either brain hemisphere profit from information obtained before take off and while flying over the release site. The existence and degree of lateralization is discussed in comparison to other studies that investigated homing under monocular viewing conditions.

Animals↗
PubMed1998

Relationship between selected orientation rest frame, circular vection and space motion sickness.

Space motion sickness (SMS) and spatial orientation and motion perception disturbances occur in 70-80% of astronauts. People select "rest frames" to create the subjective sense of spatial orientation. In microgravity, the astronaut's rest frame may be based on visual scene polarity cues and on the internal head and body z axis (vertical body axis). The data reported here address the following question: Can an astronaut's orientation rest frame be related and described by other variables including circular vection response latencies and space motion sickness? The astronaut's microgravity spatial orientation rest frames were determined from inflight and postflight verbal reports. Circular vection responses were elicited by rotating a virtual room continuously at 35 degrees/s in pitch, roll and yaw with respect to the astronaut. Latency to the onset of vection was recorded from the time the crew member opened their eyes to the onset of vection. The astronauts who used visual cues exhibited significantly shorter vection latencies than those who used internal z axis cues. A negative binomial regression model was used to represent the observed total SMS symptom scores for each subject for each flight day. Orientation reference type had a significant effect, resulting in an estimated three-fold increase in the expected motion sickness score on flight day 1 for astronauts who used visual cues. The results demonstrate meaningful classification of astronauts' rest frames and their relationships to sensitivity to circular vection and SMS. Thus, it may be possible to use vection latencies to predict SMS severity and duration.

Adult↗
PubMed2003

Mathematical analysis of a correlation-based model for orientation map formation.

We consider a correlation-based model for the orientation map formation proposed by Miller [Journal of Neuroscience 14 (1994) 409] and study the formation mathematically. We perform the Fourier transform and compute the principal component of the model. With our analysis, the roles of functions are clarified and the result indicates that the developed orientation maps have the following properties. (1) Maps have oriented receptive fields. (2) Preferred orientations smoothly change on the cortical surface. (3) Periodicity of preferred orientations does not appear. (4) Periodicity of phases appears. (5) Singular points appear irregularly on the cortical surface. Our analytical results are justified by computer simulations.

Algorithms↗
PubMed2001

Prediction of orientation selectivity from receptive field architecture in simple cells of cat visual cortex.

From the intracellularly recorded responses to small, rapidly flashed spots, we have quantitatively mapped the receptive fields of simple cells in the cat visual cortex. We then applied these maps to a feedforward model of orientation selectivity. Both the preferred orientation and the width of orientation tuning of the responses to oriented stimuli were well predicted by the model. Where tested, the tuning curve was well predicted at different spatial frequencies. The model was also successful in predicting certain features of the spatial frequency selectivity of the cells. It did not successfully predict the amplitude of the responses to drifting gratings. Our results show that the spatial organization of the receptive field can account for a large fraction of the orientation selectivity of simple cells.

Action Potentials↗
PubMed2003

Dynamics of orientation selectivity in the primary visual cortex and the importance of cortical inhibition.

To test theories of orientation selectivity in primary visual cortex (V1), we have done experiments to measure the dynamics of orientation tuning of single neurons in the V1 cortex of macaque monkeys. Based on our dynamics results, we propose that a V1 cell's orientation selectivity is generated mainly by both tuned enhancement and global suppression. Enhancement near the preferred orientation is probably caused by feed-forward input from LGN (plus amplification by cortical-cortical interaction). Global suppression could be supplied by cortical inhibition. Additionally, in about 1/3 of V1 neurons (usually the most sharply tuned) there is tuned suppression, centered near the cell's preferred orientation but broader than tuned enhancement. These mechanisms also can explain important features of steady-state selectivity in the V1 neuron population. Furthermore, similar neuronal mechanisms may be used generally throughout the cerebral cortex.

Animals↗
PubMed1999

Neuroanatomic contributions to slowed orienting of attention in children with autism.

Previous research has demonstrated that adult autistic patients are abnormally slow to orient attention, with degree of slowed orienting associated with severity of cerebellar hypoplasia. This research was extended to children who, at ages two through six, met diagnostic criteria for autism and underwent magnetic resonance imaging (MRI). An average of 3 years later, when old enough to participate in behavioral experiments, the children returned to the laboratory and completed a spatial attention paradigm. Degree of slowed attentional orienting to visual cues was significantly correlated with degree of cerebellar hypoplasia, but not with size of other neuroanatomic regions. Additionally, there was a trend for orienting speed to differ between diagnostic outcome subgroups; children with confirmed diagnoses of autism at time of behavioral testing had larger orienting deficits than those who no longer met diagnostic criteria for autism. This research is among the first to establish a specific brain-behavior link in autistic children.

Atrophy↗