tailieunhanh - Visual perception - part 3

Thay đổi trong phản ứng dân số gây ra bởi những thay đổi trong tốc độ kích thích kinh tế. (a) hình ảnh khác biệt, lớp phủ đường viền (hình chiều rộng ¼ mm), và các chức năng điều chỉnh dân số thu được với 451 kích thích kết cấu di chuyển theo chiều ngang ở ba tốc độ: 101 / s (đỉnh ¼ 691), 501 / s (cao điểm ¼ 421) | 128 b 10 sec Speed of stimulus sec Fig. 5. Shifts in the population response induced by changes in stimulus speed. a Difference images contour overlays inset width mm and population tuning functions obtained with 45 texture stimuli moving horizontally at three speeds 10 peak 69 50 s peak 42 and 100 s peak 14 . b Average population responses 7 SEM for three speeds n 7 animals the peak shifts from 73 at low speed to 47 at intermediate speed to 17 at high speed. c The peak of best-fit Gaussian function to population tuning functions for textures drifting at 10 different speeds 10-100 s at 10 intervals are plotted against stimulus speed R2 of regression line . Reproduced with permission from Macmillan Magazines. In an attempt to acquire a better understanding of these relationships we developed a program that calculates the 3-D power spectrum of a moving stimulus and the response of a set of realistic receptive field envelopes to that spectrum in real-time. This program available at can show interactively and in 3-D how changes to a stimulus features such as line length motion axis or speed affect its power spectrum and how these changes in turn affect the activation of the receptive field envelopes. The problem of understanding the population response to moving 2-D stimuli can also be approached in the space domain as opposed to the frequency domain using a Gabor function as a V1 receptive field model. DeAngelis et al. 1993 Jones and Palmer 1987 . We modeled the population response using eight different Gabor 129 functions with different orientations as described in more detail below each Gabor acting as a proxy for a cortical column with similar response properties. We computed the population response of our entire filter bank consisting of eight filters to a given stimulus and have reported the result as a population tuning function to be compared directly in its shape to the optically derived tuning functions shown earlier. The .