Representation of spatial frequency and orientation in the visual cortex

Knowledge of the response of the primary visual cortex to the various spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of spatial frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and spatial frequencies. We found that (i) the optical responses to all orientations and spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for spatial frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our spatial frequency data revealed a cortical map that continuously assigns different optimal spatial frequency responses to different cortical locations over the entire spatial frequency range.     

Representation of frequency in memory.

A review of the literature indicates that although event frequency is known to have many behavioral consequences, the intervening representation process(es) are not well understood. Storage of frequency information poses a number of theoretical and methodological problems. 4 hypotheses regarding frequency representation are distinguished (trace-strength, multiple-trace, numerical inference, and multiple-process), and evidence from previous experiments using verbal, nonverbal, and nonstimulus events is evaluated. None of the proposed models can be ruled out entirely, although the multiple-trace hypothesis offers the best explanation for data obtained from "verbal" studies. Unfortunately, nearly all the data collected to date involve verbal stimuli and traditional verbal-learning paradigms, raising the question of representativeness. If frequency can be stored other than by trace multiplexing, it would most likely show up in other event domains. Acquisition of frequency information is typically by incidental means, making such factors as set, task characteristics, and event composition (i.e., anything that could control attention during acquisition) doubly important. It is argued that any real understanding of basic frequency mechanisms must await an expanded scope of investigation. (54 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychohysical hallucinations of orientation and spatial frequency

After inspection of vertical sinusoidal gratings at least three distinct types of subjective or "hallucinated" patterns can be seen on a uniform test field. One type, here called horizontal streaming (H), is already well-known from the work of MacKay. A second type (V) looks like aroughly sinusoidal grating about 1-5 octaves above the adapting spitial frequency. Under optimal conditions a second vertical component appears at about 2 octaves below the adapting frequency. The third category of aftereffect consists of diagonal lines (D) at two orientations (about +/-40 degrees from vertical). The spatial-frequency band at these two orientations appears to be fairly broad, but roughly similar to the adapting frequency. The duration and strength of D increased, while V declined, at higher adapting spatial frequencies. D and V were increasing functions of adapting contrast, while H appeared abruptly only after the highest adapting contrast. H, D, and V are thus all functionally distinct. A schematic model of cortical organization is proposed to account for these phenomena. Pattern channels selective for a given orientation are grouped together with movement channels selective for the orthogonal direction. Antagonism between channels within such "modules" accounts for the streaming effect (H). Inhibition between modules tuned to different orientations and spatial frequencies accounts for the D and V effects: after adaptation of channels in one module, neighbouring module(s) are released from inhibition to produce a spurious response which is seen as a grating-like object in the adapted part of the visual field. During flickering adaptation a "halluncinated" lattice can be seen superimposed on the adapting grating. It apparently consists of Fourier components more remote from the adapting pattern than D and V are. This disinhibitory effect is strong confirmation of the inhibitory model. The regular and highly organized matrix of channels implied by these experiments may constitute a cortical hypercolumn conducting a coarse, piecewise Fourier transformation of the retinal image.     

Subjective landmarks in perception and memory for spatial location.

Four experiments involving 125 undergraduates investigated the use of cognitive strategies for encoding spatial location in visual figures. Ss reproduced the position of a dot in a square figure that had distance markers placed along 2 sides. Ss' responses were biased toward imaginary points of intersection formed by the distance markers when Ss responded from memory (Exp 1) or while viewing the figures (Exp 2). Findings demonstrate that empty regions of a figure can serve as subjective landmarks for spatial localization. In Exp 3, dot relocation was similarly distorted toward physical cross marks placed at the intersections of distance markers. The attraction of dots to intersection points depended on the viewer employing a strategy of mentally projecting from distance markers to form imaginary intersections. In Exp 4, attraction toward intersection points was observed only when Ss employed the projection strategy. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Children's spatial analysis of hierarchical patterns: Construction and perception.

Two experiments were reported that aimed at investigating the development of spatial analysis of hierarchical patterns in children between 3 and 9 years of age. A total of 108 children participated in the drawing experiment, and 224 children were tested in a force-choice similarity judgment task. In both tasks, participants were exposed to consistent and inconsistent targets for short (300-ms) and long (3-s) durations. The drawing task showed that 3-year-old children either preferred to draw the local level or reproduced both levels in a nonintegrated manner. Coordination between the 2 processes started to emerge at 4 years of age, and 6-year-old children produced essentially correct integrated responses. The similarity judgment task confirmed that local processing dominated at 3 years of age. Preference for global processing appeared at 5 years of age, and it gained in strength later. Significant effects of stimulus consistency and stimulus duration were also found. In particular, the use of inconsistent patterns in the similarity judgment task revealed a phenomenon of local-to-global interference in the 3-year-olds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of eccentricity and spatial frequency on the orientation discrimination asymmetry

This study investigated the effects of eccentricity and spatial frequency on the discrimination of vertical and oblique (10 deg from vertical) Gabor patches. Within a display stimuli were scaled by a factor F = 1 + E/E2 at each eccentricity (E) in an attempt to equate either the number of photoreceptors (E2 = 2.5) or cortical area (E2 = 0.77) engaged at each eccentricity. The task was to detect a differently oriented target among eleven distractors. Orientation discrimination asymmetries (ODAs) were found such that an oblique stimulus was easier to detect in a background of vertical stimuli than vice versa. Subjects were equally sensitive to the two highest frequency Gabor patches and less sensitive to the lowest frequency Gabors. When stimuli were scaled with E2 = 2.5 sensitivity was constant at all eccentricities and the ODA magnitude was unaffected. When stimuli were magnified with E2 = 0.77 both sensitivity and ODA magnitude increased with eccentricity. Generally, we may conclude that the ODA effect is not a strictly foveal phenomenon nor is it a strictly high frequency effect.     

Uncertainty experiments support the roles of second-order mechanisms in spatial frequency and orientation discriminations

Previous studies of spatial frequency and orientation discrimination [Vision Res. 32, 1885 (1992)] suggest the existence of two second-order cortical mechanisms: one that mediates spatial frequency discriminations and sums signals across orientations and one that mediates orientation discriminations and sums signals across spatial frequency bands. The existence of each mechanism is tested in an uncertainty experiment in which the observer does not know which of two hypothetically pooled signals deviates from the standard but must judge whether the deviation is an increment or a decrement. No uncertainty effect is expected if the signals are completely pooled. Observed effects are compared with this expectation and with both theoretical and empirical estimates of the effects expected if the signals are processed separately. Results support the existence of the first mechanism, but not its exclusive role in mediating spatial frequency judgments, and support the exclusive role of the second mechanism in mediating orientation judgments.     

Phenomenology of attention: I. Color, location, orientation, and spatial frequency.

The effect of attention on the phenomenal appearance of objects was investigated in the domains of color (hue), location, line orientation, and spatial frequency. Observers indicated the appearance of a briefly presented above-threshold stimulus by selecting a matching stimulus along a sensory continuum (e.g., color). Attention was manipulated with a dual task that involved letter identification. Attention had little effect in changing the way objects appeared in terms of observers' mean response. However, in each stimulus domain, attention reduced the variability of responses. It is argued that attention should be viewed in terms of reducing uncertainty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature asymmetries in visual search: effects of display duration, target eccentricity, orientation and spatial frequency

In Experiments 1-3, we monitored search performance as a function of target eccentricity under display durations that either allowed or precluded eye movements. The display was present either until observers responded, for 104 msec, or for 62 msec. In all three experiments an orientation asymmetry emerged: observers detected a tilted target among vertical distracters more efficiently than a vertical target among vertical distracters. As target eccentricity increased, reaction times and errors augmented, and the set size effect became more pronounced, more so for vertical than tilted targets. In Experiments 4-7, the stimulus spatial properties were manipulated: spatial frequency; size; and orientation. The eccentricity effect was more pronounced for vertical than tilted targets and for high- than low-spatial frequency targets. This effect was eliminated when either the size, the size and orientation, or the size and spatial frequency were magnified (M-cortical factor). By increasing the signal-to-noise ratio, magnification reduced the extent of both asymmetries; it aided more the detection of tilted than vertical and of high- than low-spatial frequency targets. Experiments 4-7 indicate that performance improvement in the magnified conditions was due to the specific pairing of stimulus size with retinal eccentricity and not to the larger stimulus size of the magnified conditions. We conclude that stimulus size, orientation and spatial frequency influence the extent of the eccentricity effect and the efficiency of search performance.     

Representation of order information: An analysis of grouping effects in short-term memory.

Exps I–IV tested the independence model, 2 hierarchical models, and the dependence model of matrix relationships with a probed recall procedure in which 91 undergraduates were presented with a grouped sequence of items and were then required to recall the position and group of 1 of the items. This technique provided information about how well Ss correctly recalled both the group and position, the group only, the position only, and neither the group nor the position of an item. Findings reveal that when the items in a group were letters, digits, or musical notes, the data conformed to a hierarchical structure. When the nonalphanumeric characters were used, a matrix structure emerged. Exps V–VII required 50 undergraduates to judge the dissimilarity of 2 sequences of grouped items, the 2nd of which (the variation) was a reordering of the 1st (the original). The variation was made by reordering the groups in the original, reordering positions within groups, or reordering both groups and positions. Results show that when the members of a group were able to be encoded as single verbal units, the data supported a hierarchical system. When this was not possible, a matrix system fitted the data best. It is concluded that there is no general code for representing the order of grouped sequences and that the results are more compatible with a theory that postulates a number of specific subsystems in short-term memory, each with its own format for preserving order, than one that assumes a generalized order code. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dominance as a factor in interpersonal choice and perception.

The hypotheses herein tested were that a person chooses to interact with, and tends to perceive other people in terms of the complement of his own degree of dominance. Ss were shown a movie depicting the interaction between 4 people, 2 of whom displayed dominant behavior, 2, submissive. Measures of the Ss' own dominance were compared with their answers on a sociometric questionnaire which elicited Ss' preference for the actors. The results failed to support the hypotheses as stated. The findings were discussed in terms of their possible meaning, and their relationship to other findings. 25 refs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Judgments of frequency and recognition memory in a multiple-trace memory model.

The multiple-trace simulation model, {minerva} 2, was applied to a number of phenomena found in experiments on relative and absolute judgments of frequency, and forced-choice and yes–no recognition memory. How the basic model deals with effects of repetition, forgetting, list length, orientation task, selective retrieval, and similarity and how a slightly modified version accounts for effects of contextual variability on frequency judgments were shown. Two new experiments on similarity and recognition memory were presented, together with appropriate simulations; attempts to modify the model to deal with additional phenomena were also described. Questions related to the representation of frequency are addressed, and the model is evaluated and compared with related models of frequency judgments and recognition memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representation of space in blind persons: Vision as a spatial sense?

Some researchers of studies of the incidence of early visual experience on spatial abilities have demonstrated profound spatial deficits in early blind participants, whereas others have not found evidence of deleterious effects of early visual deprivation. The aims of this article are to (a) consider the theoretical background of these studies, (b) take stock of the divergent data, and (c) propose new means of investigation. The authors examine the reasons why vision plays a critical role in spatial cognition. They review the literature data. They also review the factors that could account for the discrepant data and the effects of the lack of early visual experience on brain functioning. They propose that the study of strategies is a valuable option to obtain insight into early blind persons' spatial impairment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory enhances visual perception: Evidence from signal detection analysis.

We show that perceptual sensitivity to visual stimuli can be modulated by matches between the contents of working memory (WM) and stimuli in the visual field. Observers were presented with an object cue (to hold in WM or to merely attend) and subsequently had to identify a brief target presented within a colored shape. The cue could be re-presented in the display, where it surrounded either the target (on valid trials) or a distractor (on invalid trials). Perceptual identification of the target, as indexed by A′, was enhanced on valid relative to invalid trials but only when the cue was kept in WM. There was minimal effect of the cue when it was merely attended and not kept in WM. Verbal cues were as effective as visual cues at modulating perceptual identification, and the effects were independent of the effects of target saliency. Matches to the contents of WM influenced perceptual sensitivity even under conditions that minimized competition for selecting the target. WM cues were also effective when targets were less likely to fall in a repeated WM stimulus than in other stimuli in the search display. There were no effects of WM on decisional criteria, in contrast to sensitivity. The findings suggest that reentrant feedback from WM can affect early stages of perceptual processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the modularity of recognition memory for object form and spatial location: a topographic ERP analysis

Event-related potentials from 61 scalp sites were used to examine the brain processes subserving recognition memory for object forms and spatial locations. Subjects memorized line drawings of highly familiar objects and their spatial locations within a two-dimensional matrix. Prior to the test phases a cue indicated whether object-based or spatially-based recognition judgements were required. Recognition judgements were faster and more accurate for spatially-based than for object-based judgements. A variety of topographical differences in the ERP waveforms as a function of recognition task emerged: First, when the cue indicated that object-based judgements were required, negative slow wave activity extending for several hundred ms with a maximum at frontal recording sites was obtained. Conversely when spatially-based judgements were required, slow wave activity developed over parieto-occipital areas. Second, early portions of the old/new effects evoked by the test items (i.e. 300-600 ms after stimulus onset) showed a similar anterior-posterior dissociation as a function of recognition task. Third, for object-based, but not for spatially-based, judgements, late old/new effects (i.e. 700-1600 ms) were found with a clear maximum at right frontal recordings. The results are consistent with the view that functionally and anatomically different brain systems are involved in recognition memory for object form and spatial location. They further suggest that the retrieval of object forms involves conceptual semantic integration processes.     

Emotional perception and memory in amnesia.

The authors examined whether perception of emotional stimuli is normal in amnesia and whether emotional arousal has the same enhancing effect on memory in amnesic patients as it has in healthy controls. Forty standardized color pictures were presented while participants rated each picture according to emotional intensity (arousal) and pleasantness (valence). An immediate free-recall test was given for the pictures, followed by a yes-no recognition test. Arousal and valence ratings were highly similar among the amnesic patients and controls. Emotional arousal (regardless of valence) enhanced both recall and recognition of the pictures, and this enhancement was proportional for amnesic patients and controls. Results suggest that emotional perception and the enhancing effect of emotional arousal on memory are intact in amnesia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A principal components analysis of dynamic spatial memory biases.

Research has shown that spatial memory for moving targets is often biased in the direction of implied momentum and implied gravity, suggesting that representations of the subjective experiences of these physical principles contribute to such biases. The present study examined the association between these spatial memory biases. Observers viewed targets that moved horizontally from left to right before disappearing or viewed briefly shown stationary targets. After a target disappeared, observers indicated the vanishing position of the target. Principal components analysis revealed that biases along the horizontal axis of motion loaded on separate components from biases along the vertical axis orthogonal to motion. The findings support the hypothesis that implied momentum and implied gravity biases have unique influences on spatial memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social perception and sociometric choice of children.

"This study was designed to test the generality of the positive relationship between perceived similarity and valuation of others." The results indicate that highest sociometric choices tend to be perceived as more similar to self than are lowest sociometric choices and also more similar to self than they actually are. The proposition is suggested that the positive relationship between perceived similarity and valuation of others is a function of the need to be similar to valued persons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of spatial orientation in infancy.

The ability of infants at 6, 11, and 16 mo to keep track of their relationship to a place in space was assessed in 4 experiments with 72 Ss. Ss were trained to expect an event to occur to their right or left; they were then moved so that their view of the space was reversed. The direction in which they turned in anticipation of the event indicated whether they were coding the location egocentrically or objectively. In Exp I, a longitudinal study of 24 infants, significant shift with age from egocentric responding at 6 and 11 mo to objective responding at 16 mo was revealed, a change that data in Exp II indicated was not simply due to previous experience with the experimental space. In Exps III and IV, manipulation of the type of experience Ss had during training failed to decrease egocentric responding at 6 and 11 mo. The overall pattern indicated that a landmark had its greatest impact at 11 mo. The data support Piaget's theory that in coding location, young infants rely on past accommodations to an object rather than its relationship to other objects or the larger space. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estradiol enhances learning and memory in a spatial memory task and effects levels of monoaminergic neurotransmitters

Calretinin (CaR) is a calcium-binding protein that is distributed extensively in the central nervous system. It is localized in the cell bodies and neurites of specific neuronal populations and serves, therefore, as a reliable anatomical marker. Some components of the pretectocerebellar projection, which connects specific pretectal nuclei to caudal cerebellar folia, are concerned with the cerebellar control of visual reflexes. We investigated the distribution of pretectocerebellar-projecting neurons in relation to cells that show CaR immunoreactivity. Cells that project to the cerebellar cortex in the diencephalic primary visual nuclei and in other grisea, like the nucleus spiriformis medialis and the nucleus dorsofrontalis, colocalized with those that appeared to be immunolabeled intensely with anti-CaR antiserum. To explore the hypothesis of a common developmental origin of these pretectal cerebellopetal neurons, we also investigated the development of CaR-immunopositive cells in the chick pretectum and the arrival of their fibers in the cerebellum, from 10 days of incubation (stage 36) to posthatching stages. Finally, we analyzed the source of CaR+ climbing fibers and found a subpopulation of CaR+ cells in the inferior olivary nucleus. On the whole, these results suggest that there is a common developmental origin of pretectal cerebellopetal neurons, some of which share the property of CaR expression. The functional significance of this correlation needs to be investigated.