The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Ehud Kaplan - One of the best experts on this subject based on the ideXlab platform.
-
representation of Spatial Frequency and orientation in the visual cortex
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Richard M Everson, A K Prashanth, Michael Gabbay, Bruce W Knight, Lawrence Sirovich, Ehud KaplanAbstract:Knowledge of the response of the primary visual cortex to the various Spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of Spatial Frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and Spatial frequencies. We found that (i) the optical responses to all orientations and Spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for Spatial Frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our Spatial Frequency data revealed a cortical map that continuously assigns different optimal Spatial Frequency responses to different cortical locations over the entire Spatial Frequency range.
Robert W. Mccarley - One of the best experts on this subject based on the ideXlab platform.
-
Spatial Frequency discrimination in schizophrenia
Journal of Abnormal Psychology, 2002Co-Authors: Brian F Odonnell, Kiriaki C Stylianopoulos, Geoffrey F. Potts, Paul G Nestor, Martha E. Shenton, Robert W. MccarleyAbstract:Pathways within the visual system can be distinguished on the basis of selectivity for low or high Spatial frequencies. Spatial Frequency discrimination was evaluated in 17 medicated male patients with schizophrenia and 19 male control subjects. Subjects were required to discriminate whether pairs of high contrast, sinusoidally modulated gratings were the same or different in Spatial Frequency. Accuracy performance was compared at high, medium, and low Spatial frequencies on tasks matched for control performance. Patients showed a greater performance decrement of 12% on low as compared with 4% on high Spatial frequencies. These findings suggest a disturbance of right hemisphere mechanisms involved in Spatial perception and attention in schizophrenia.
Richard M Everson - One of the best experts on this subject based on the ideXlab platform.
-
representation of Spatial Frequency and orientation in the visual cortex
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Richard M Everson, A K Prashanth, Michael Gabbay, Bruce W Knight, Lawrence Sirovich, Ehud KaplanAbstract:Knowledge of the response of the primary visual cortex to the various Spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of Spatial Frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and Spatial frequencies. We found that (i) the optical responses to all orientations and Spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for Spatial Frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our Spatial Frequency data revealed a cortical map that continuously assigns different optimal Spatial Frequency responses to different cortical locations over the entire Spatial Frequency range.
Ted Maddess - One of the best experts on this subject based on the ideXlab platform.
-
Low-Spatial-Frequency Channels and the Spatial Frequency-Doubling Illusion
Investigative ophthalmology & visual science, 2008Co-Authors: Yanti Rosli, Suzanne M Bedford, Ted MaddessAbstract:PURPOSE This study examined the number and nature of spatiotemporal channels in the region where the Frequency-doubling (FD) illusion would be expected to occur at eight locations spanning the central 30 degrees of the visual field. METHODS The probability of seeing the FD illusion was examined in 17 subjects. Stimuli were presented at 5 octaves of low Spatial frequencies, at each of seven flicker frequencies in the range 5.65 to 27.95 Hz. In a single trial, subjects matched the apparent Spatial Frequency of the flickering test pattern using a two-alternative, forced-choice method. Thirteen subjects were examined for stimuli presented at contrast 0.95. Three or four subjects were examined at each of the contrasts 0.2, 0.4, and 0.8. A factor analysis was conducted on the psychometric functions, quantifying the number and possible spatiotemporal tuning of neural channels present. RESULTS At contrast 0.95, three factors were able to explain 79.3% of the total variance in the psychometric responses to the 35 test conditions. This simple form of three broad spatiotemporal channels was also found at the other contrasts and in different subjects. The factor scores showed differential distribution of the factors onto the eight different visual field locations. Thus the expression of the three channels differed somewhat across the visual field. CONCLUSIONS The results support earlier reports, that there are several low-Spatial-Frequency channels below 1 cyc/deg in the periphery. The results may have implications for the FDT and matrix perimeters.
Lawrence Sirovich - One of the best experts on this subject based on the ideXlab platform.
-
representation of Spatial Frequency and orientation in the visual cortex
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Richard M Everson, A K Prashanth, Michael Gabbay, Bruce W Knight, Lawrence Sirovich, Ehud KaplanAbstract:Knowledge of the response of the primary visual cortex to the various Spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of Spatial Frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and Spatial frequencies. We found that (i) the optical responses to all orientations and Spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for Spatial Frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our Spatial Frequency data revealed a cortical map that continuously assigns different optimal Spatial Frequency responses to different cortical locations over the entire Spatial Frequency range.
