Peripheral positional acuity: Retinal and cortical constraints on 2-dot separation discrimination under photopic and scotopic conditions

Yap, Yen Lee; Levi, Dennis M.; Klein, Stanley A.

doi:10.1016/0042-6989(89)90091-6

Cited by 44 publications

(2 citation statements)

References 39 publications

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“…Six of the seven subjects were able to discriminate Gabors separated by 0.19 deg in eccentricity, and all seven subjects were able to discriminate differences of 0.77 deg eccentricity (lowest d′ was 1.2 for subject MC). The precision with which subjects judged Gabor locations is consistent with several previous studies on acuity in the periphery [11], [12], [13], even in absence of references [14]. Further, these psychophysical data confirm previous reports that the method of single stimuli can be used to measure acuity even though subjects must rely on an implicit standard when judging each stimulus [10], [15], [16].…”

Section: Resultssupporting

confidence: 90%

Negative BOLD fMRI Response in the Visual Cortex Carries Precise Stimulus-Specific Information

2007

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Sustained positive BOLD (blood oxygen level-dependent) activity is employed extensively in functional magnetic resonance imaging (fMRI) studies as evidence for task or stimulus-specific neural responses. However, the presence of sustained negative BOLD activity (i.e., sustained responses that are lower than the fixation baseline) has remained more difficult to interpret. Some studies suggest that it results from local “blood stealing” wherein blood is diverted to neurally active regions without a concomitant change of neural activity in the negative BOLD regions. However, other evidence suggests that negative BOLD is a result of local neural suppression. In both cases, regions of negative BOLD response are usually interpreted as carrying relatively little, if any, stimulus-specific information (hence the predominant reliance on positive BOLD activity in fMRI). Here we show that the negative BOLD response resulting from visual stimulation can carry high information content that is stimulus-specific. Using a general linear model (GLM), we contrasted standard flickering stimuli to a fixation baseline and found regions of the visual cortex that displayed a sustained negative BOLD response, consistent with several previous studies. Within these negative BOLD regions, we compared patterns of fMRI activity generated by flickering Gabors that were systematically shifted in position. As the Gabors were shifted further from each other, the correlation in the spatial pattern of activity across a population of voxels (such as the population of V1 voxels that displayed a negative BOLD response) decreased significantly. Despite the fact that the BOLD signal was significantly negative (lower than fixation baseline), these regions were able to discriminate objects separated by less than 0.5 deg (at ∼10 deg eccentricity). The results suggest that meaningful, stimulus-specific processing occurs even in regions that display a strong negative BOLD response.

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Section: Resultssupporting

confidence: 90%

Negative BOLD fMRI Response in the Visual Cortex Carries Precise Stimulus-Specific Information

2007

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“…Rods comprise 95% of photoreceptors in the retina and 90% of photoreceptors in the macula (Curcio, Sloan, Kalina, & Hendrickson, 1990; Dubra et al, 2011), but we know very little about how spatial information is processed by rod-mediated pathways. The few studies that have investigated spatial vision under scotopic conditions (Duffy & Hubel, 2007; Livingstone & Hubel, 1994; Mandelbaum & Sloan, 1947; Yap, Levi, & Klein, 1989; Zele & Cao, 2014) reveal that rods signal the brain on the same or parallel pathways to cones, but that they have larger receptive fields and operate on a larger spatial scale. Some retinal ganglion cells may even adjust their receptive field tunings depending on light level (Yao et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Scotopic contour and shape discrimination using radial frequency patterns

Flynn

Jeffrey

2019

Journal of Vision

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Radial frequency (RF) patterns are valuable tools for investigations of contour integration and shape discrimination. Under photopic conditions, healthy observers can detect deformations from circularity in RF patterns as small as 3 seconds of arc. Such fine discrimination may be facilitated by cortical curvature detectors or global shape-detecting mechanisms that favor a closed contour. Rods make up 95% of photoreceptors in the retina, but we know very little about how spatial information is processed by rod-mediated pathways. We measured scotopic radial deformation discrimination using both full and partly occluded RF pattern stimuli. We found radial deformation thresholds of around 2–3 minutes of arc for stimuli with a wide range of radii and RFs. When parts of the stimulus were occluded, scotopic thresholds improved up to the point that three or four cycles of modulation were visible; no further improvement occurred with the addition of more visible cycles. When only one to three cycles were visible, an increase in curvature per cycle became important, allowing observers to detect smaller deformations from circularity. Our results indicate that the scotopic radial deformation thresholds for the stimuli tested are not dependent on global circularity cues but are instead mediated by local curvature cues.

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The Spatial Resolution of Visual Attention

Intriligator

Cavanagh

2001

Cognitive Psychology

658

582

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Two tasks were used to evaluate the grain of visual attention, the minimum spacing at which attention can select individual items. First, observers performed a tracking task at many viewing distances. When the display subtended less than 1 degrees in size, tracking was no longer possible even though observers could resolve the items and their motions: The items were visible but could not be individuated one from the other. The limiting size for selection was roughly the same whether tracking one or three targets, suggesting that the resolution limit acts independently of the capacity limit of attention. Second, the closest spacing that still allowed individuation of single items in dense, static displays was examined. This critical spacing was about 50% coarser in the radial direction compared to the tangential direction and was coarser in the upper as opposed to the lower visual field. The results suggest that no more than about 60 items can be arrayed in the central 30 degrees of the visual field while still allowing attentional access to each individually. Our data show that selection has a coarse grain, much coarser than visual resolution. These measures of the resolution of attention are based solely on the selection of location and are not confounded with preattentive feature interactions that may contribute to measures from flanker and crowding tasks. The results suggest that the parietal area is the most likely locus of this selection mechanism and that it acts by pointing to the spatial coordinates (or cortical coordinates) of items of interest rather than by holding a representation of the items themselves.

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Peripheral positional acuity: Retinal and cortical constraints on 2-dot separation discrimination under photopic and scotopic conditions

Cited by 44 publications

References 39 publications

Negative BOLD fMRI Response in the Visual Cortex Carries Precise Stimulus-Specific Information

Negative BOLD fMRI Response in the Visual Cortex Carries Precise Stimulus-Specific Information

Scotopic contour and shape discrimination using radial frequency patterns

The Spatial Resolution of Visual Attention

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