The missing pathway in current visuospatial processing models

Spatial configuration learning depends on the parahippocampal place area (PPA), a functionally heterogenous area which current visuo-spatial processing models place downstream from parietal cortex and area V4 of early visual cortex (EVC). Here, we present evidence for the medial occipital longitudinal tract (MOLT), a novel white matter pathway connecting the PPA with EVC earlier than V4. By using multimodal imaging and neuropsychological assessments in the unique case of Patient 1, we demonstrate that an occipital stroke sparing the PPA but disconnecting the MOLT can lead to chronic deficits in configuration learning. Further, through an advanced, data-driven clustering analysis of diffusion MRI structural connectivity in a large control cohort, we demonstrate that the PPA sits at the confluence of the MOLT and the parieto-medial-temporal branch of the dual-stream model. The MOLT may therefore support multi-stage learning of object configuration by allowing direct reciprocal exchange between the PPA and EVC.

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Peaked Encoding of Relative Luminance in Macaque Areas V1 and V2

Journal of Neurophysiology ◽

10.1152/jn.00793.2004 ◽

2005 ◽

Vol 93 (3) ◽

pp. 1620-1632 ◽

Cited By ~ 43

Author(s):

Xinmiao Peng ◽

David C. Van Essen

Keyword(s):

Light Adaptation ◽

Spatial Configuration ◽

Color Space ◽

Three Dimensional ◽

Luminance Level ◽

Adaptation Level ◽

Luminance Change ◽

Color Preferences ◽

Related Information ◽

Early Visual Cortex

It is widely presumed that throughout the primate visual pathway neurons encode the relative luminance of objects (at a given light adaptation level) using two classes of monotonic function, one positively and the other negatively sloped. Based on computational considerations, we hypothesized that early visual cortex also contains neurons preferring intermediate relative luminance values. We tested this hypothesis by recording from single neurons in areas V1 and V2 of alert, fixating macaque monkeys during presentation of a large, spatially uniform patch oscillating slowly in luminance and surrounded by a static texture background. A substantial subset of neurons responsive to such low spatial frequency luminance stimuli in both areas exhibited prominent and statistically reliable response peaks to intermediate rather than minimal or maximal luminance values. When presented with static patches of different luminance but of the same spatial configuration, most neurons tested retained a preference for intermediate relative luminance. Control experiments using luminance modulation at multiple low temporal frequencies or reduced amplitude indicate that in the slow luminance-oscillating paradigm, responses were more strongly modulated by the luminance level than the rate of luminance change. These results strongly support our hypothesis and reveal a striking cortical transformation of luminance-related information that may contribute to the perception of surface brightness and lightness. In addition, we tested many luminance-sensitive neurons with large chromatic patches oscillating slowly in luminance. Many cells, including the gray-preferring neurons, exhibited strong color preferences, suggesting a role of luminance-sensitive cells in encoding information in three-dimensional color space.

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Mental Imagery Follows Similar Cortical Reorganization as Perception: Intra-Modal and Cross-Modal Plasticity in Congenitally Blind

Cerebral Cortex ◽

10.1093/cercor/bhy151 ◽

2018 ◽

Vol 29 (7) ◽

pp. 2859-2875 ◽

Cited By ~ 3

Author(s):

A W de Borst ◽

B de Gelder

Keyword(s):

Visual Cortex ◽

Mental Imagery ◽

Cortical Plasticity ◽

Tactile Perception ◽

Cortical Reorganization ◽

Area V4 ◽

Congenitally Blind ◽

Early Visual Cortex ◽

Blind Individuals ◽

Discriminative Patterns

Abstract Cortical plasticity in congenitally blind individuals leads to cross-modal activation of the visual cortex and may lead to superior perceptual processing in the intact sensory domains. Although mental imagery is often defined as a quasi-perceptual experience, it is unknown whether it follows similar cortical reorganization as perception in blind individuals. In this study, we show that auditory versus tactile perception evokes similar intra-modal discriminative patterns in congenitally blind compared with sighted participants. These results indicate that cortical plasticity following visual deprivation does not influence broad intra-modal organization of auditory and tactile perception as measured by our task. Furthermore, not only the blind, but also the sighted participants showed cross-modal discriminative patterns for perception modality in the visual cortex. During mental imagery, both groups showed similar decoding accuracies for imagery modality in the intra-modal primary sensory cortices. However, no cross-modal discriminative information for imagery modality was found in early visual cortex of blind participants, in contrast to the sighted participants. We did find evidence of cross-modal activation of higher visual areas in blind participants, including the representation of specific-imagined auditory features in visual area V4.

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Shape Representation in Area V4: Position-Specific Tuning for Boundary Conformation

Journal of Neurophysiology ◽

10.1152/jn.2001.86.5.2505 ◽

2001 ◽

Vol 86 (5) ◽

pp. 2505-2519 ◽

Cited By ~ 254

Author(s):

Anitha Pasupathy ◽

Charles E. Connor

Keyword(s):

Shape Representation ◽

Single Type ◽

Complex Objects ◽

Axis Orientation ◽

Area V4 ◽

Multi Stage ◽

Complex Boundary ◽

Concave Boundary ◽

The Right ◽

Shape Tuning

Visual shape recognition in primates depends on a multi-stage pathway running from primary visual cortex (V1) to inferotemporal cortex (IT). The mechanisms by which local shape signals from V1 are transformed into selectivity for abstract object categories in IT are unknown. One approach to this issue is to investigate shape representation at intermediate stages in the pathway, such as area V4. We studied 109 V4 cells that appeared sensitive to complex shape in preliminary tests. To achieve a more complete picture of shape representation in V4, we tested each cell with a set of 366 stimuli, constructed by systematically combining convex and concave boundary elements into closed shapes. Using this large, diverse stimulus set, we found that all the cells in our sample responded to a wide variety of shapes and did not appear to encode any single type of global shape. However, for most cells the shapes evoking strongest responses were characterized by a consistent type of boundary conformation at a specific position within the stimulus. For example, a given cell might be tuned for shapes containing concave curvature at the right, with other parts of the shape having little or no effect on responses. Many cells were tuned for more complex boundary configurations (e.g., a convex angle adjacent to a concave curve). We quantified this kind of shape tuning with Gaussian functions on a curvature × position domain. These tuning functions fit the neural responses much better than tuning functions based on edge or axis orientation. Thus individual V4 cells appear to encode moderately complex boundary information at specific locations within larger shapes. This finding suggests that, at intermediate stages in the V1-IT transformation, complex objects are represented at least partly in terms of the configurations and positions of their contour components.

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Perceptual Learning of Simple Stimuli Modifies Stimulus Representations in Posterior Inferior Temporal Cortex

Journal of Cognitive Neuroscience ◽

10.1162/jocn_a_00641 ◽

2014 ◽

Vol 26 (10) ◽

pp. 2187-2200 ◽

Cited By ~ 16

Author(s):

Hamed Zivari Adab ◽

Ivo D. Popivanov ◽

Wim Vanduffel ◽

Rufin Vogels

Keyword(s):

Visual Cortex ◽

Perceptual Learning ◽

Single Unit ◽

Brain Plasticity ◽

Temporal Cortex ◽

Adult Brain ◽

Orientation Discrimination ◽

Area V4 ◽

Early Visual Cortex ◽

Visual Cortical

Practicing simple visual detection and discrimination tasks improves performance, a signature of adult brain plasticity. The neural mechanisms that underlie these changes in performance are still unclear. Previously, we reported that practice in discriminating the orientation of noisy gratings (coarse orientation discrimination) increased the ability of single neurons in the early visual area V4 to discriminate the trained stimuli. Here, we ask whether practice in this task also changes the stimulus tuning properties of later visual cortical areas, despite the use of simple grating stimuli. To identify candidate areas, we used fMRI to map activations to noisy gratings in trained rhesus monkeys, revealing a region in the posterior inferior temporal (PIT) cortex. Subsequent single unit recordings in PIT showed that the degree of orientation selectivity was similar to that of area V4 and that the PIT neurons discriminated the trained orientations better than the untrained orientations. Unlike in previous single unit studies of perceptual learning in early visual cortex, more PIT neurons preferred trained compared with untrained orientations. The effects of training on the responses to the grating stimuli were also present when the animals were performing a difficult orthogonal task in which the grating stimuli were task-irrelevant, suggesting that the training effect does not need attention to be expressed. The PIT neurons could support orientation discrimination at low signal-to-noise levels. These findings suggest that extensive practice in discriminating simple grating stimuli not only affects early visual cortex but also changes the stimulus tuning of a late visual cortical area.

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Functional rather than structural connectivity explains grassland plant diversity patterns following landscape scale habitat loss

Landscape Ecology ◽

10.1007/s10980-020-01138-x ◽

2020 ◽

Author(s):

Adam Kimberley ◽

Danny Hooftman ◽

James M. Bullock ◽

Olivier Honnay ◽

Patricia Krickl ◽

...

Keyword(s):

Functional Connectivity ◽

Habitat Loss ◽

Green Infrastructure ◽

Large Scale ◽

Spatial Configuration ◽

Landscape Connectivity ◽

Natural Habitat ◽

Structural Connectivity ◽

Species Dispersal ◽

Generalist Species

Abstract Context Functional connectivity is vital for plant species dispersal, but little is known about how habitat loss and the presence of green infrastructure interact to affect both functional and structural connectivity, and the impacts of each on species groups. Objectives We investigate how changes in the spatial configuration of species-rich grasslands and related green infrastructure such as road verges, hedgerows and forest borders in three European countries have influenced landscape connectivity, and the effects on grassland plant biodiversity. Methods We mapped past and present land use for 36 landscapes in Belgium, Germany and Sweden, to estimate connectivity based on simple habitat spatial configuration (structural connectivity) and accounting for effective dispersal and establishment (functional connectivity) around focal grasslands. We used the resulting measures of landscape change to interpret patterns in plant communities. Results Increased presence of landscape connecting elements could not compensate for large scale losses of grassland area resulting in substantial declines in structural and functional connectivity. Generalist species were negatively affected by connectivity, and responded most strongly to structural connectivity, while functional connectivity determined the occurrence of grassland specialists in focal grasslands. Restored patches had more generalist species, and a lower density of grassland specialist species than ancient patches. Conclusions Protecting both species rich grasslands and dispersal pathways within landscapes is essential for maintaining grassland biodiversity. Our results show that increases in green infrastructure have not been sufficient to offset loss of semi-natural habitat, and that landscape links must be functionally effective in order to contribute to grassland diversity.

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The Effect of Nonlinear Amplitude Growth on the Speech Perception Benefits Provided by a Single-Sided Vocoder

Journal of Speech Language and Hearing Research ◽

10.1044/2018_jslhr-h-18-0001 ◽

2019 ◽

Vol 62 (3) ◽

pp. 745-757 ◽

Cited By ~ 2

Author(s):

Jessica M. Wess ◽

Joshua G. W. Bernstein

Keyword(s):

Transfer Functions ◽

Spatial Configuration ◽

Free Field ◽

Spatial Separation ◽

Compression And Expansion ◽

Interaural Difference ◽

Interaural Differences ◽

Single Sided Deafness ◽

Perceptual Separation ◽

Loudness Growth

PurposeFor listeners with single-sided deafness, a cochlear implant (CI) can improve speech understanding by giving the listener access to the ear with the better target-to-masker ratio (TMR; head shadow) or by providing interaural difference cues to facilitate the perceptual separation of concurrent talkers (squelch). CI simulations presented to listeners with normal hearing examined how these benefits could be affected by interaural differences in loudness growth in a speech-on-speech masking task.MethodExperiment 1 examined a target–masker spatial configuration where the vocoded ear had a poorer TMR than the nonvocoded ear. Experiment 2 examined the reverse configuration. Generic head-related transfer functions simulated free-field listening. Compression or expansion was applied independently to each vocoder channel (power-law exponents: 0.25, 0.5, 1, 1.5, or 2).ResultsCompression reduced the benefit provided by the vocoder ear in both experiments. There was some evidence that expansion increased squelch in Experiment 1 but reduced the benefit in Experiment 2 where the vocoder ear provided a combination of head-shadow and squelch benefits.ConclusionsThe effects of compression and expansion are interpreted in terms of envelope distortion and changes in the vocoded-ear TMR (for head shadow) or changes in perceived target–masker spatial separation (for squelch). The compression parameter is a candidate for clinical optimization to improve single-sided deafness CI outcomes.

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