Biology subjects

Kiorpes, L.

Publications and source records attributed to Kiorpes, L..

7 recordsLinked to original sources

bioRxiv2026

Curvature tuning in areas V2 and V4 of the developing macaque

Visual areas V2 and V4 are critical for the perception of visual forms in primates. Neurons in area V4 of macaque monkeys are often sensitive to the curvature of specific boundary segments within shapes, but it is unknown how curvature tuning is represented in the developing brain. To address this, we recorded multiunit neural activity from areas V2 and V4 of two macaque monkeys, at both 30 and 58 weeks of age, in response to shape stimuli which primarily varied in curvature along a single segment. Observable curvature tuning was adult-like from 30 weeks of age in both V2 and V4. We compared the tuning of sites to shapes presented at multiple positions. We saw evidence of position-invariant tuning in V4, but not in V2. Position invariance in V4 was stable from 30 weeks of age. Finally, we fit two models - a stimulus-centric model of boundary curvature tuning, and a simple linear model based on the spike-triggered average response to all stimuli. We found many sites in both V2 and V4 whose responses could be captured by one or both models, but no evidence of age-related changes in curvature tuning within the space of either model. Our results suggest that the neural representation of curvature in both areas reaches maturity soon after birth, and that object-centric representations of curvature first emerge in V4, not V2.

neuroscience↗

bioRxiv2025

Neural sensitivity to radial frequency patterns in the visual cortex of developing macaques

Visual resolution, contrast sensitivity and form perception improve gradually with age. In nonhuman primates, the sensitivity and resolution of cells in the retina, lateral geniculate nucleus and primary visual cortex (V1) also improve, but not enough to account for the perceptual changes. So, what aspects of visual system development limit visual sensitivity in infants? Improvements in behavioral sensitivity might arise from maturation of regions downstream of V1 such as V2, V4 and pIT, which are thought to support increasingly complex perceptual abilities. We recorded the responses of populations of neurons in areas V1, V2, V4, and pIT to radial frequency patterns - a type of global form stimulus. Subjects were three young monkeys between the ages of 19 and 54 weeks, and a single adult animal. We found that neurons and neural populations in V4 reliably encoded global form in radial frequency stimuli at the earliest ages we studied, while V1 neurons do not. V2 and pIT populations also showed some degree of selectivity for these patterns at early ages, especially at higher radial frequency values. We did not find significant, systematic changes in neural decoding performance that could account for the improvement in behavioral performance over the same age range in an overlapping group of animals (Rodriguez Deliz et al., 2024). Finally, consistent with our prior behavioral results, neural populations in V4 show highest sensitivity for the higher radial frequency values which contain the highest concentration of curvature and orientation cues. SIGNIFICANCE STATEMENTInfants have remarkably limited ability to discriminate shapes. These limitations cannot be fully explained by postnatal changes in their eyes, visual thalamus, or primary visual cortex. The perception of shape requires integration of local cues across space to create global form information. We therefore examined populations of neurons in extrastriate visual cortex to learn whether information represented in these regions might limit infants abilities to process global forms. We found instead that extrastriate areas involved in global form processing function maturely early in life, by the age of 4-6 months, suggesting that infants perceptual limits are set by other aspects of brain development.

neuroscience↗

bioRxiv2025

Emergence of a contrast-invariant representation of naturalistic texture in macaque visual cortex

Sensory stimuli vary across a variety of dimensions, like contrast, orientation, or texture. The brain must rely on population representations to distinguish changes in one dimension from changes in another. To understand how the visual system might extract separable stimulus representations, we recorded multiunit neuronal responses to texture images varying along two dimensions: contrast, a property represented as early as the retina, and naturalistic statistical structure, a property that modulates neuronal responses in V2 and V4, but not in V1. We measured how sites in these 3 cortical areas responded to variation in both dimensions. Contrast modulated responses in all areas. In V2 and V4, the presence of naturalistic structure both modulated responses and increased contrast sensitivity. Tuning for naturalistic structure was both strongest and most dispersed in V4. We measured how well populations in each area could support the linear readout of both dimensions. Populations in V2 and V4 could support the linear readout of naturalistic structure, but in V4, this readout was more robust to variations in contrast. Significance StatementTo support flexible behavior, the brain must simultaneously represent different stimulus dimensions. Single neurons are typically modulated by multiple dimensions, and so cannot distinguish them - they must be extracted by decoding neural populations. We studied neuronal responses in three cortical visual areas - V1, V2, V4 - using texture images varying in both contrast and naturalistic image structure. We used population decoders to read out each dimension. In all areas, contrast was well decoded independently of image structure. On the other hand, V1 could not decode image structure independent of contrast, while V2 and V4 could. V4 decoding was greatly superior, because the selectivity of individual sites for texture was more diverse than in V1 or V2.

neuroscience↗

bioRxiv2024

Responses to visual motion of neurons in the extrastriate visual cortex of macaque monkeys with experimental amblyopia

Amblyopia is a developmental disorder that results from abnormal visual experience in early life. Amblyopia typically reduces visual performance in one eye. We studied the representation of visual motion information in area MT and nearby extrastriate visual areas in two monkeys made amblyopic by creating an artificial strabismus in early life, and in a single age-matched control monkey. Tested monocularly, cortical responses to moving dot patterns, gratings, and plaids were qualitatively normal in awake, fixating amblyopic monkeys, with primarily subtle differences between the eyes. However, the number of binocularly driven neurons was substantially lower than normal; of the neurons driven predominantly by one eye, the great majority responded only to stimuli presented to the fellow eye. The small population driven by the amblyopic eye showed reduced coherence sensitivity and a preference for faster speeds in much the same way as behavioral deficits. We conclude that, while we do find important differences between neurons driven by the two eyes, amblyopia does not lead to a large scale reorganization of visual receptive fields in the dorsal stream when tested through the amblyopic eye, but rather creates a substantial shift in eye preference toward the fellow eye.

neuroscience↗

bioRxiv2024

Developmentally stable representations of naturalistic image structure in macaque visual cortex

We studied visual development in macaque monkeys using texture stimuli, matched in local spectral content but varying in "naturalistic" structure. In adult monkeys, naturalistic textures preferentially drive neurons in areas V2 and V4, but not V1. We paired behavioral measurements of naturalness sensitivity with separately-obtained neuronal population recordings from neurons in areas V1, V2, V4, and inferotemporal cortex (IT). We made behavioral measurements from 16 weeks of age and physiological measurements as early as 20 weeks, and continued through 56 weeks. Behavioral sensitivity reached half of maximum at roughly 25 weeks of age. Neural sensitivities remained stable from the earliest ages tested. As in adults, neural sensitivity to naturalistic structure increased from V1 to V2 to V4. While sensitivities in V2 and IT were similar, the dimensionality of the IT representation was more similar to V4s than to V2s.

neuroscience↗

bioRxiv2024

Development of radial frequency pattern perception in macaque monkeys

Infant primates see poorly, and most perceptual functions mature steadily beyond early infancy. Behavioral studies on human and macaque infants show that global form perception, as measured by the ability to integrate contour information into a coherent percept, improves dramatically throughout the first several years after birth. However, it is unknown when sensitivity to curvature and shape emerges in early life. We studied the development of shape sensitivity in eighteen macaques, aged 2 months to 10 years. Using radial frequency stimuli (RFS), circular targets whose radii are modulated sinusoidally, we tested monkeys ability to discriminate RFS from circles as a function of the depth and frequency of sinusoidal modulation. We implemented a new 4-choice oddity task and compared the resulting data with that from a traditional 2-alternative task. Behavioral performance at all radial frequencies improved with age. Performance was better for higher radial frequencies, suggesting the developing visual system prioritizes processing of fine visual details that are ecologically relevant. By utilizing two complementary methods, we were able to capture a comprehensive developmental trajectory for shape perception.

neuroscience↗

bioRxiv2019

Altered functional interactions between neurons in primary visual cortex of macaque monkeys with experimental amblyopia

Amblyopia, a disorder in which vision through one of the eyes is degraded, arises because of defective processing of information by the visual system. Amblyopia often develops in humans after early misalignment of the eyes (strabismus), and can be simulated in macaque monkeys by artificially inducing strabismus. In such amblyopic animals, single-unit responses in primary visual cortex (V1) are appreciably reduced when evoked by the amblyopic eye compared to the other (fellow) eye. However, this degradation in single V1 neuron responsivity is not commensurate with the marked losses in visual sensitivity and resolution measured behaviorally. Here we explored the idea that changes in patterns of coordinated activity across populations of V1 neurons may contribute to degraded visual representations in amblyopia, potentially making it more difficult to read out evoked activity to support perceptual decisions. We studied the visually-evoked activity of V1 neuronal populations in three macaques (M. nemestrina) with strabismic amblyopia and in one control. Activity driven through the amblyopic eye was diminished, and these responses also showed more interneuronal correlation at all stimulus contrasts than responses driven through the fellow eye or responses in the control. A decoding analysis showed that responses driven through the amblyopic eye carried less visual information than other responses. Our results suggest that part of the reduced visual capacity of amblyopes may be due to changes in the patterns of functional interaction among neurons in V1.\n\nNew and noteworthyAmblyopia is a developmental disorder of visual processing that reduces visual function and changes the visual responses of cortical neurons in macaque monkeys. The neuronal and behavioral changes are not always well correlated. We found that the interactions among neurons in the visual cortex of monkeys with amblyopia are also altered. These changes may contribute to amblyopic visual deficits by diminishing the amount of information relayed by neuronal populations driven by the amblyopic eye.

neuroscience↗