Class Information Predicts Activation by Object Fragments in Human Object Areas

2008 ◽  
Vol 20 (7) ◽  
pp. 1189-1206 ◽  
Author(s):  
Yulia Lerner ◽  
Boris Epshtein ◽  
Shimon Ullman ◽  
Rafael Malach
Keyword(s):  
Classification Performance ◽  
Blood Oxygenation ◽  
Imaging Studies ◽  
Behavioral Studies ◽  
Visual Areas ◽  
Human Object ◽  
Oxygenation Level ◽  
Class Information ◽  
High Level ◽  
Object Features

Object-related areas in the ventral visual system in humans are known from imaging studies to be preferentially activated by object images compared with noise or texture patterns. It is unknown, however, which features of the object images are extracted and represented in these areas. Here we tested the extent to which the representation of visual classes used object fragments selected by maximizing the information delivered about the class. We tested functional magnetic resonance imaging blood oxygenation level-dependent activation of highly informative object features in low- and high-level visual areas, compared with noninformative object features matched for low-level image properties. Activation in V1 was similar, but in the lateral occipital area and in the posterior fusiform gyrus, activation by “informative” fragments was significantly higher for three object classes. Behavioral studies also revealed high correlation between performance and fragments information. The results show that an objective class-information measure can predict classification performance and activation in human object-related areas.

Effect of Luminance Contrast on BOLD fMRI Response in Human Primary Visual Areas

1998 ◽  
Vol 79 (4) ◽  
pp. 2204-2207 ◽  
Author(s):  
Bradley G. Goodyear ◽  
Ravi S. Menon
Keyword(s):  
Luminance Contrast ◽  
Blood Oxygenation ◽  
Planar Imaging ◽  
Bold Fmri ◽  
Activation Level ◽  
Red Led ◽  
Visual Areas ◽  
Oxygenation Level ◽  
Fmri Response ◽  
Image Pixels

Goodyear, Bradley G. and Ravi S. Menon. Effect of luminance contrast on BOLD fMRI response in human primary visual areas. J. Neurophysiol. 79: 2204–2207, 1998. In this study, we examined the effect of stimulus luminance contrast on blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging within human visual cortex (V1 and extrastriate). Between experiments, the calibrated luminance of a single red LED covering 2° of the subject's visual field was changed relative to a constant background luminance. This stimulus provided a different foveal luminance contrast for each experiment. We used an echo planar imaging sequence to collect blood-oxygenation-sensitive images during and in the absence of the presented stimulus. Our results showed that within V1 there was an increase in the spatial extent of activation with increasing stimulus contrast, but no trend was seen within extrastriate. In both V1 and extrastriate, the local mean activation level for all activated image pixels remained constant with increasing luminance contrast. However, when we investigated activated pixels common to all luminance contrast levels, we found that there was an increase in the mean activation level within V1, but not within extrastriate. These results suggest that there is an increase in the activity of cells in V1 with increasing luminance contrast.

BOLD fMRI Response of Early Visual Areas to Perceived Contrast in Human Amblyopia

2000 ◽  
Vol 84 (4) ◽  
pp. 1907-1913 ◽  
Author(s):  
Bradley G. Goodyear ◽  
David A. Nicolle ◽  
G. Keith Humphrey ◽  
Ravi S. Menon
Keyword(s):  
Spatial Frequency ◽  
Neuronal Response ◽  
Blood Oxygenation ◽  
Normal Vision ◽  
Staircase Method ◽  
Visual Areas ◽  
Oxygenation Level ◽  
Fmri Response ◽  
Visual Cortical ◽  
Contrast Thresholds

In this study, we used a temporal two-alternative forced choice psychophysical procedure to measure the observer's perception of a 22% physical contrast grating for each eye as a function of spatial frequency in four subjects with unilateral amblyopia and in six subjects with normal vision. Contrast thresholds were also measured using a standard staircase method. Additionally, blood-oxygenation-level–dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to measure the neuronal response within early visual cortical areas to monocular presentations of the same 22% physical contrast gratings as a function of spatial frequency. For all six subjects with normal vision and for three subjects with amblyopia, the psychophysically measured perception of 22% contrast as a function of spatial frequency was the same for both eyes. Threshold contrast, however, was elevated for the amblyopic eye for all subjects, as expected. The magnitude of the fMRI response to 22% physical contrast within “activated” voxels was the same for each eye as a function of spatial frequency, regardless of the presence of amblyopia. However, there were always fewer “activated” fMRI voxels during amblyopic stimulation than during normal eye stimulation. These results are consistent with the hypotheses that contrast thresholds are elevated in amblyopia because fewer neurons are responsive during amblyopic stimulation, and that the average firing rate of the responsive neurons, which reflects the perception of contrast, is unaffected in amblyopia.

scholarly journals Unique Neural Activity Patterns Among Lower Order Cortices and Shared Patterns Among Higher Order Cortices During Processing of Similar Shapes With Different Stimulus Types

i-Perception ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 204166952110182
Author(s):  
Zhen Li ◽  
Hiroaki Shigemasu
Keyword(s):  
Classification Accuracy ◽  
Stimulus Type ◽  
Activity Patterns ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Black And White ◽  
Visual Areas ◽  
Oxygenation Level ◽  
Element Type ◽  
3D Shapes

We investigated the neural mechanism of the processing of three-dimensional (3D) shapes defined by disparity and perspective. We measured blood oxygenation level-dependent signals as participants viewed and classified 3D images of convex–concave shapes. According to the cue (disparity or perspective) and element type (random dots or black and white dotted lines), three types of stimuli were used: random dot stereogram, black and white dotted lines with perspective, and black and white dotted lines with binocular disparity. The blood oxygenation level-dependent images were then classified by multivoxel pattern analysis. To identify areas selective to shape, we assessed convex–concave classification accuracy with classifiers trained and tested using signals evoked by the same stimulus type (same cue and element type). To identify cortical regions with similar neural activity patterns regardless of stimulus type, we assessed the convex–concave classification accuracy of transfer classification in which classifiers were trained and tested using different stimulus types (different cues or element types). Classification accuracy using the same stimulus type was high in the early visual areas and subregions of the intraparietal sulcus (IPS), whereas transfer classification accuracy was high in the dorsal subregions of the IPS. These results indicate that the early visual areas process the specific features of stimuli, whereas the IPS regions perform more generalized processing of 3D shapes, independent of a specific stimulus type.

Differential Contribution of Early Visual Areas to the Perceptual Process of Contour Processing

2004 ◽  
Vol 91 (4) ◽  
pp. 1716-1721 ◽  
Author(s):  
Mark M. Schira ◽  
Manfred Fahle ◽  
Tobias H. Donner ◽  
Antje Kraft ◽  
Stephan A. Brandt
Keyword(s):  
Discrimination Task ◽  
Visual Awareness ◽  
Blood Oxygenation ◽  
Signal Modulation ◽  
Contextual Modulation ◽  
Central Figure ◽  
Retinotopic Mapping ◽  
Visual Areas ◽  
Oxygenation Level

We investigated contour processing and figure–ground detection within human retinotopic areas using event-related functional magnetic resonance imaging (fMRI) in 6 healthy and naïve subjects. A figure (6° side length) was created by a 2nd-order texture contour. An independent and demanding foveal letter-discrimination task prevented subjects from noticing this more peripheral contour stimulus. The contour subdivided our stimulus into a figure and a ground. Using localizers and retinotopic mapping stimuli we were able to subdivide each early visual area into 3 eccentricity regions corresponding to 1) the central figure, 2) the area along the contour, and 3) the background. In these subregions we investigated the hemodynamic responses to our stimuli and compared responses with or without the contour defining the figure. No contour-related blood oxygenation level–dependent modulation in early visual areas V1, V3, VP, and MT+ was found. Significant signal modulation in the contour subregions of V2v, V2d, V3a, and LO occurred. This activation pattern was different from comparable studies, which might be attributable to the letter-discrimination task reducing confounding attentional modulation. In V3a, but not in any other retinotopic area, signal modulation corresponding to the central figure could be detected. Such contextual modulation will be discussed in light of the recurrent processing hypothesis and the role of visual awareness.

scholarly journals Compressive spatial summation in human visual cortex

2013 ◽  
Vol 110 (2) ◽  
pp. 481-494 ◽  
Author(s):  
Kendrick N. Kay ◽  
Jonathan Winawer ◽  
Aviv Mezer ◽  
Brian A. Wandell
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Object Representation ◽  
Spatial Summation ◽  
Blood Oxygenation ◽  
Population Responses ◽  
Visual Areas ◽  
Oxygenation Level ◽  
Restricted Region ◽  
Extrastriate Areas

Neurons within a small (a few cubic millimeters) region of visual cortex respond to stimuli within a restricted region of the visual field. Previous studies have characterized the population response of such neurons using a model that sums contrast linearly across the visual field. In this study, we tested linear spatial summation of population responses using blood oxygenation level-dependent (BOLD) functional MRI. We measured BOLD responses to a systematic set of contrast patterns and discovered systematic deviation from linearity: the data are more accurately explained by a model in which a compressive static nonlinearity is applied after linear spatial summation. We found that the nonlinearity is present in early visual areas (e.g., V1, V2) and grows more pronounced in relatively anterior extrastriate areas (e.g., LO-2, VO-2). We then analyzed the effect of compressive spatial summation in terms of changes in the position and size of a viewed object. Compressive spatial summation is consistent with tolerance to changes in position and size, an important characteristic of object representation.

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