How does global visual context affect the primary visual cortex?

According to predictive coding theories, why should the detection of structural regularities lead to decreased activity in V1?

Structural regularities allow higher cortical levels to predict incoming sensory data more efficiently, reducing prediction error and thus decreasing V1 activity.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Which neural connections correspond to the spatial extent of the high-contrast summation field (hsRF) in V1?

The spatial extent of the high-contrast summation field (hsRF) is consistent with the terminations of forward connections.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Which neural connections are consistent with the spatial extent of the low-contrast summation field (lsRF) in V1?

The spatial extent of the low-contrast summation field (lsRF) is consistent with horizontal (lateral) connections.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Why can't horizontal connections alone account for the spatial scale and timing of the full surround suppression field?

The spatial extent and slow conduction velocities of horizontal connections are insufficient, implying that backward projections from extra-striate cortex must mediate these full effects.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What are the two distinct components of the extra-classical receptive field (ECRF) surround, and what connections do they depend on?

The ECRF surround consists of a 'proximal' component depending on horizontal connections and a 'distal' component depending on inter-areal backward connections.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Why was the minimum distance between the stimulus components set to 3° in this study?

It exceeded the mean proximal surround field of V1 (~2.3°), biasing the experiment away from horizontal connections and towards testing feedback-mediated extra-classical effects.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How did the study ensure that individual V1 classical receptive fields were only stimulated by a single moving dot?

The stimulus elements were kept at a minimum of 3° apart, which is larger than the average human V1 receptive field width across the 2.3° to 16.3° eccentricity range.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

In the incoherent motion condition, what constraint was placed on neighboring components to prevent regional patterns?

No more than one immediate neighbor was allowed to share the same direction of motion and orientation, excluding randomly selected regionally coherent motion.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What incidental task did subjects perform during the scanning sessions to maintain their attentional set?

Subjects were instructed to press a button when any of the stimulus components turned red.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Did eye movements differ significantly between the coherent and incoherent motion conditions?

No, there were no significant differences in eye movement amplitudes or spectral profiles between the two motion conditions.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What was the main BOLD response effect in the striate cortex during coherent motion compared to incoherent motion?

There was a significant decrease (suppression) in the visually evoked BOLD response in the striate cortex during coherent motion.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How did human V5/MT respond during coherent relative to incoherent motion?

Human V5/MT showed a decreased visually evoked BOLD response (suppression) during coherent motion.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Which brain regions showed increased activation (enhancement) during coherent motion?

The right extra-striate cortex (near the V1/V2 border) and the bilateral posterior cingulate gyrus (pCG) showed increased BOLD responses.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Where was the maximum of the enhanced extra-striate cortical response localized using the cytoarchitectonic probability atlas?

The maximum activation was located on the border between V1 and V2.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Why is concurrent suppression of some visual areas and enhancement of others theoretically important?

Representational/predictive coding theories predict concurrent suppression of subordinate areas (such as V1) and enhanced responses in supra-ordinate areas representing global context.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How do conduction velocities of horizontal connections compare to forward and backward connections?

Conduction velocities of horizontal connections are approximately 10 times slower than forward and backward connections.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How do the V5/MT findings of this study differ from studies using high component density (e.g., Rees et al.)?

High density studies showed positive linear increases in V5/MT with motion coherence, whereas this sparse-stimulus study found a relative decrease in V5/MT response during coherent motion.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Why is V2 considered the first level of hierarchical processing capable of integrating the contextual information in this sparse stimulus?

Because V2 receptive fields are larger (~twice V1 size), allowing peripheral V2 units to receive sensory input from more than one stimulus element.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What anatomical difference in inter-hemispheric connectivity exists between V1 and V2 that could aid global integration?

There are virtually no extra-foveal inter-hemispheric connections at the level of V1, whereas there are a large number of commissural fibers between V2 areas.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What anatomical route bypasses V1 and could explain why V5/MT and V1 show similar low-level response profiles?

Direct projection pathways from the lateral geniculate nucleus (LGN) to V5/MT bypass V1, accounting for about 10% of geniculate projections in macaque.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What does latency research reveal about the arrival of visual signals in V5/MT compared to V1?

Visual signals arrive in V5/MT only a few milliseconds after or sometimes even before they arrive in V1.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How might the posterior cingulate gyrus (pCG) anatomically exert top-down influence on V5/MT despite lacking direct connections?

Via indirect connections passing through areas in the superior temporal sulcus (such as the posterior part of area TPO), which receives pCG inputs and projects to V5/MT.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What was a key limitation of the visual stimulus design regarding eccentricity and receptive field scaling?

The inter-dot spacing was not adjusted to scale up with retinal eccentricity, which may have allowed larger extrastriate receptive fields at peripheral locations to encompass multiple dots.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How do the findings of this study compare to the fMRI results of Murray et al. (2002)?

Murray et al. also found V1 suppression accompanied by increased activity in higher visual areas (LOC) when visual elements were grouped into coherent shapes.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

How do macaque V5/MT receptive field sizes compare to V1 receptive fields in terms of scale and overlap?

V5/MT receptive fields are much larger (~5° near fovea to ~30° in periphery) and feature a 10–15° overlap with the ipsilateral hemisphere.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

What are the estimated feedback coupling sizes from V2, V3, and MT to V1 cells?

Feedback coupling spans ~5° from V2, ~10° from V3, and ~27° from V5/MT.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI · quote verified

Why can't a direct comparison be made between this study's findings and MT cooling inactivation studies in macaques?

Macaque cooling studies showed reduced V1 surround suppression under MT inactivation, whereas this study observed relative suppression of V1 during relative decreases in V5/MT activity.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI

What is the main overall conclusion of this study regarding inferential theories of perception?

Global percepts (motion coherence) influence local processing at subordinate levels (V1) via backward feedback connections, lending support to hierarchical predictive coding models.

Source: Extra-classical receptive field effects measured in striate cortex with fMRI · DOI