Foveal Cortex Research Articles

On the relationship between foveal mask interference and mental imagery in peripheral object recognition.

A delayed foveal mask affects perception of peripheral stimuli. The effect is determined by the timing of the mask and by the similarity with the peripheral stimulus. A congruent mask enhances performance, while an incongruent one impairs it. It is hypothesized that foveal masks disrupt a feedback mechanism reaching the foveal cortex. This mechanism could be part of a broader circuit associated with mental imagery, but this hypothesis has not as yet been tested. We investigated the link between mental imagery and foveal feedback. We tested the relationship between performance fluctuations caused by the foveal mask-measured in terms of discriminability (d') and criterion (C)-and the scores from two questionnaires designed to assess mental imagery vividness (VVIQ) and another exploring object imagery, spatial imagery and verbal cognitive styles (OSIVQ). Contrary to our hypotheses, no significant correlations were found between VVIQ and the mask's impact on d' and C. Neither the object nor spatial subscales of OSIVQ correlated with the mask's impact. In conclusion, our findings do not substantiate the existence of a link between foveal feedback and mental imagery. Further investigation is needed to determine whether mask interference might occur with more implicit measures of imagery.

Foveal feedback in perceptual processing: Contamination of neural representations and task difficulty effects.

Visual object recognition was traditionally believed to rely on a hierarchical feedforward process. However, recent evidence challenges this notion by demonstrating the crucial role of foveal retinotopic cortex and feedback signals from higher-level visual areas in processing peripheral visual information. The nature of the information conveyed through foveal feedback remains a topic of debate. To address this, we conducted a study employing a foveal mask paradigm with varying stimulus-mask onset asynchronies in a peripheral same/different task, where peripheral objects exhibited different degrees of similarity. Our hypothesis posited that simultaneous arrival of feedback and mask information in the foveal cortex would lead to neural contamination, biasing perception. Notably, when the two peripheral objects were identical, we observed a significant increase in the number of "different" responses, peaking at approximately 100 ms. Similar effect was found when the objects were dissimilar, but with an overall later timing (around 150 ms). No significant difference was found when comparing easy (dissimilar objects) and difficult trials (similar objects). The findings challenge the hypothesis that foveation planning alone accounts for the observed effects. Instead, these and previous observations support the notion that the foveal cortex serves as a visual sketchpad for maintaining and manipulating task-relevant information.

The Role of Foveal Cortex in Discriminating Peripheral Stimuli: The Sketchpad Hypothesis.

Foveal (central) and peripheral vision are strongly interconnected to provide an integrated experience of the world around us. Recently, it has been suggested that there is a feedback mechanism that links foveal and peripheral vision. This peripheral-to-foveal feedback differs from other feedback mechanisms in that during visual processing a novel representation of a stimulus is formed in a different cortical region than that of the feedforward representation. The functional role of foveal feedback is not yet completely understood, but some evidence from neuroimaging studies suggests a link with peripheral shape processing. Behavioural and transcranial magnetic stimulation studies show impairment in peripheral shape discrimination when the foveal retinotopic cortex is disrupted post stimulus presentation. This review aims to link these findings to the visual sketchpad hypothesis. According to this hypothesis, foveal retinotopic cortex stores task-relevant information to aid identification of peripherally presented objects. We discuss how the characteristics of foveal feedback support this hypothesis and rule out other possible explanations. We also discuss the possibility that the foveal feedback may be independent of the sensory modality of the stimulation.

Investigating the role of the foveal cortex in peripheral object discrimination

Peripheral object discrimination is hindered by a central dynamic mask presented between 150 and 300 ms after stimulus onset. The mask is thought to interfere with task-relevant feedback coming from higher visual areas to the foveal cortex in V1. Fan et al. (2016) supported this hypothesis by showing that the effect of mask can be further delayed if the task requires mental manipulation of the peripheral target. The main purpose of this study was to better characterize the temporal dynamics of foveal feedback. Specifically, in two experiments we have shown that (1) the effect of foveal noise mask is sufficiently robust to be replicated in an online data collection (2) in addition to a change in sensitivity the mask affects also the criterion, which becomes more conservative; (3) the expected dipper function for sensitivity approximates a quartic with a global minimum at 94 ms, while the best fit for criterion is a quintic with a global maximum at 174 ms; (4) the power spectrum analysis of perceptual oscillations in sensitivity data shows a cyclic effect of mask at 3 and 12 Hz. Overall, our results show that foveal noise affects sensitivity in a cyclic manner, with a global dip emerging earlier than previously found. The noise also affects the response bias, even though with a different temporal profile. We, therefore, suggest that foveal noise acts on two distinct feedback mechanisms, a faster perceptual feedback followed by a slower cognitive feedback.

Object categorization in visual periphery is modulated by delayed foveal noise.

Behavioral studies in humans indicate that peripheral vision can do object recognition to some extent. Moreover, recent studies have shown that some information from brain regions retinotopic to visual periphery is somehow fed back to regions retinotopic to the fovea and disrupting this feedback impairs object recognition in human. However, it is unclear to what extent the information in visual periphery contributes to human object categorization. Here, we designed two series of rapid object categorization tasks to first investigate the performance of human peripheral vision in categorizing natural object images at different eccentricities and abstraction levels (superordinate, basic, and subordinate). Then, using a delayed foveal noise mask, we studied how modulating the foveal representation impacts peripheral object categorization at any of the abstraction levels. We found that peripheral vision can quickly and accurately accomplish superordinate categorization, while its performance in finer categorization levels dramatically drops as the object presents further in the periphery. Also, we found that a 300-ms delayed foveal noise mask can significantly disturb categorization performance in basic and subordinate levels, while it has no effect on the superordinate level. Our results suggest that human peripheral vision can easily process objects at high abstraction levels, and the information is fed back to foveal vision to prime foveal cortex for finer categorizations when a saccade is made toward the target object.

Decoding action intention from the activity pattern in the Foveal Cortex

Decoding action intention from the activity pattern in the Foveal Cortex

Temporally flexible feedback signal to foveal cortex for peripheral object recognition

Recent studies have shown that information from peripherally presented images is present in the human foveal retinotopic cortex, presumably because of feedback signals. We investigated this potential feedback signal by presenting noise in fovea at different object-noise stimulus onset asynchronies (SOAs), whereas subjects performed a discrimination task on peripheral objects. Results revealed a selective impairment of performance when foveal noise was presented at 250-ms SOA, but only for tasks that required comparing objects' spatial details, suggesting a task- and stimulus-dependent foveal processing mechanism. Critically, the temporal window of foveal processing was shifted when mental rotation was required for the peripheral objects, indicating that the foveal retinotopic processing is not automatically engaged at a fixed time following peripheral stimulation; rather, it occurs at a stage when detailed information is required. Moreover, fMRI measurements using multivoxel pattern analysis showed that both image and object category-relevant information of peripheral objects was represented in the foveal cortex. Taken together, our results support the hypothesis of a temporally flexible feedback signal to the foveal retinotopic cortex when discriminating objects in the visual periphery.

Reorganization of visual processing in macular degeneration is not specific to the "preferred retinal locus"

Recent work has shown that foveal cortex, deprived of its normal bottom-up input as a result of macular degeneration (MD), begins responding to stimuli presented to a peripheral retinal location. However, these studies have only presented stimuli to the “preferred retinal location,” or PRL, a spared part of the peripheral retina used by individuals with MD for fixating, face recognition, reading, and other visual tasks. Thus, previous research has not yet answered a question critical for understanding the mechanisms underlying this reorganization: Does formerly foveal cortex respond only to stimuli presented at the PRL, or does it also respond to other peripheral locations of similar eccentricity? If foveal cortex responds to stimuli at PRL because it is the long-term habitual use of this region as a functional fovea that drives the formerly foveal cortex to respond to stimuli presented at the PRL (the “use-dependent reorganization” hypothesis), then foveal cortex will not respond to stimuli presented at other locations. Alternatively, it may be that foveal cortex responds to any peripheral retinal input, independent of whether input at that retinal location has been chronically attended for months or years (the “use-independent reorganization” hypothesis). Using fMRI, we found clear activation of formerly foveal cortex to stimuli presented at either the PRL or an isoeccentric non-PRL location in two individuals with MD, supporting the use-independent reorganization hypothesis. This finding suggests that reorganization is driven by passive, not use-dependent mechanisms.

Peripheral information in foveal cortex: Generalizing across task and stimuli

Peripheral information in foveal cortex: Generalizing across task and stimuli

The role of feedback to foveal cortex in peripheral perception: ATMS study

The role of feedback to foveal cortex in peripheral perception: ATMS study

Reorganization of Visual Processing in Macular Degeneration Is Not Specific to the “Preferred Retinal Locus”

Recent work has shown that foveal cortex, deprived of its normal bottom-up input as a result of macular degeneration (MD), begins responding to stimuli presented to a peripheral retinal location. However, these studies have only presented stimuli to the "preferred retinal location," or PRL, a spared part of the peripheral retina used by individuals with MD for fixating, face recognition, reading, and other visual tasks. Thus, previous research has not yet answered a question critical for understanding the mechanisms underlying this reorganization: Does formerly foveal cortex respond only to stimuli presented at the PRL, or does it also respond to other peripheral locations of similar eccentricity? If foveal cortex responds to stimuli at PRL because it is the long-term habitual use of this region as a functional fovea that drives the formerly foveal cortex to respond to stimuli presented at the PRL (the "use-dependent reorganization" hypothesis), then foveal cortex will not respond to stimuli presented at other locations. Alternatively, it may be that foveal cortex responds to any peripheral retinal input, independent of whether input at that retinal location has been chronically attended for months or years (the "use-independent reorganization" hypothesis). Using fMRI, we found clear activation of formerly foveal cortex to stimuli presented at either the PRL or an isoeccentric non-PRL location in two individuals with MD, supporting the use-independent reorganization hypothesis. This finding suggests that reorganization is driven by passive, not use-dependent mechanisms.

The mapping of visual space onto foveal striate cortex in the macaque monkey

Visuotopic maps of foveal striate cortex have been obtained by means of single cell recordings from four hemispheres in two awake, behaving macaque monkeys. The numbers of successful separate striate penetration sites in the four hemispheres were 42, 58, 81, and 61, for a total of 242. The resolution of the maps is 10 min of visual angle, nearly an order of magnitude finer than previous maps. No striate receptive field center was found more than 5 min into the ipsilateral visual field. The four maps were sufficiently compatible with one another that they could be combined into one. There are only minor magnification differences between the right and left hemispheres and between the upper and lower quadrants. There is a vertical/horizontal magnification anisotropy of about 1.5:1 in central foveal cortex (0 to 20 min). The composite map can be approximated by the complex logarithmic equation, w = 7.7 * ln (x + iy + 0.33), where w is expressed in millimeters and x and y are expressed in degrees.

Mechanisms of static and dynamic stereopsis in foveal cortex of the rhesus monkey.

1. The sensation of stereoscopic depth rests on the central neural processing of signals evoked by the two retinal images of a single object in space. It was our purpose in this study to investigate in the behaving monkey the binocular cortical mechanisms that might underlie the ability to recognize the relative position and motion of objects in three-dimensional space.2. The large majority of neurones studied in A17 (n = 245), and all neurones studied in A18 (n = 21), were functionally connected to both eyes, and a substantial proportion (75%) of these neurones were sensitive to positional binocular disparity. On the basis of their depth sensitivity profile, four types of stereoscopic neurones were recognized, each type characteristically sensitive to visual contours appearing in depth farther than, at, or nearer than the point of binocular fixation.3. Tuned excitatory and tuned inhibitory neurones display binocular facilitation and binocular suppression respectively, to stimuli over a narrow range of small disparities, including zero disparity, with more or less pronounced reciprocal responses to stimuli with larger disparities. These neurones, the tuned excitatory in particular, may be considered to be the substrate for central fusion of slightly disparate retinal images, and to provide the basis for the neural mechanisms leading to three-dimensional perception of objects with high stereoacuity (fine stereopsis).4. Two other sets of reciprocally organized neurones, near and far neurones, respond differentially to wider ranges of crossed and uncrossed disparities. The near neurones are activated by stimuli in front of and inhibited by stimuli behind fixation. The far neurones have the reciprocal depth sensitivity. These neural elements may be regarded as active in the processing of binocular information leading to qualitative depth estimates in the presence of double vision (coarse stereopsis).5. Binocular response selectivity for the direction of object motion-in-depth depends chiefly upon monocular sensitivity to the direction of retinal image motion, a property we observed in about one half of the foveal neurones. Cortical neurones with the same directional sensitivity for monocular stimuli in both eyes display coarse binocular selectivity for the trajectory of object motion but provide unambiguous signals for the direction of motion, towards the right or towards the left within the depth domain of the neurone. A small group of neurones (3%) displays opposite and opponent directional sensitivity for stimuli in the two eyes. Their binocular response, therefore, is best when the two retinal images move in opposite directions at the same time, a condition that obtains with motion directly towards or away from the animal with little or no lateral movement. These directionally dual-opponent cells usually have coarse or no selectivity for position-in-depth.6. The results of this study indicate that basic mechanisms for the stereoscopic analysis of the position (static) and motion (dynamic) of objects in space relative to one another are present at early stages of binocular interaction in the visual cortex of primates, and that they are in effective action during normal binocular vision.

Spatial and chromatic properties of neurons subserving foveal and parafoveal vision in rhesus monkey

The response properties of neurons in the region of striate cortex subserving central retina (0°–2°) and in a region of representation of parafoveal retina (4°–7°) were studied in unanesthetized paralyzed macaque monkeys. Neurons sensitive to the orientation of the stimulus in the visual field (simple, complex and hypercomplex), and neurons lacking orientation selectivity (concentric, and a new class termed uniform) were found. In foveal cortex non-oriented cells were more numerous, and orientation sensitive cells had less strict spatial stimulus requirements than in parafoveal cortex. Most neurons received a monocular input, either exclusively or very predominantly. Three types of neurons were recognized on the basis of their responses to chromatic stimuli. (1) Luminosity neurons (about half the population) give the same qualitative response to all effective wayelengths and had a spectral sensitivity similar to that of the macaque, determined behaviorally. Cells with all spatial types of receptive fields, except simple, occurred in this group. (2) Spectrally-tuned neurons also responded in the same manner to different wavelengths, but over a narrower range than luminosity neurons, and their maximal sensitivity was shifted toward one or the other end of the visible spectrum. All tuned neurons had uniform or complex receptive field. (3) Spectrally-opponent neurons were either excited or inhibited by long wavelengths and responded in the opposite manner to short wavelengths. For cells with uniform or complex receptive fields the two opponent systems were coextensive. Simple or concentric neurons often had dual-opponent organization. The distribution of functional types among different cortical layers was similar in parafoveal and foveal cortex. The functional attributes of ocular dominance and orientation sensitivity were found to be statistically independent dimensions of cortical organization. On the other hand, the correlation between spatial and chromatic properties did not vary between different cytoarchitectonic layers, a finding suggesting that these neuronal properties depend on conjoined projectional and intracortical connecting mechanisms.