3: The Photoreceptor Mosaic

1. Human Perception 3: The Photoreceptor Mosaic

2. The Photoreceptor Types • Spatial Distribution of Receptors 3.2

3. The Photoreceptor Types • Spatial Distribution of Receptors 3.3

4. The Photoreceptor Types • Schematics 3.4

5. The Photoreceptor Types • Receptor drawings 3.5

6. The Photoreceptor Types • Cone wavelength absorptions 3.6

7. The Photoreceptor Types • Curcio et al, 1990 3.7

8. The S-cone Mosaic • Psychophysical estimation of S-cone mosaic: Williams, Macleod and Hayhoe experiments, 1981 3.8

9. The S-cone Mosaic • A biological estimate of the S-code spatial mosaic, DeMonasterio et al, 1985, just outside the fovea 3.9

10. The S-cone Mosaic: Near Periphery • A biological estimate of the S-code spatial mosaic, near periphery 3.10

11. Calculating the Viewing Angle • tan(φ)=0.0025mm/17mm=0.000147 i.e. 0.0084 degrees or 0.5 minutes or 30 seconds 3.11

12. Sampling and Aliasing • Aliasing of signals results when sampled values are the same but in-between values are not 3.12

13. Sampling and Aliasing • Harmonic undersampled all = 1:16; n = all/16; freq = 15; f = cos(2*pi*freq*n); plot(n,f,'b-o’);hold on all = 1:256; n = all/256; freq = 15; f = cos(2*pi*freq*n); plot(n,f,'r-') 3.13

14. Sampling and Aliasing • Harmonic oddly sampled clf all = 1:16; n = all/16; freq = 11.2; f = cos(2*pi*freq*n); plot(n,f,'b-o') hold on all = 1:256; n = all/256; freq = 15; f = cos(2*pi*freq*n); plot(n,f,'r-') 3.14

15. Sampling and Aliasing • Square-wave (two dimensional) aliasing • Nyquist frequency F = N/2 cos(2π(N/2+f) i/N)= cos(2π(N/2-f)i/N ) 3.15

16. The L- and M-Cone Mosaic • Perceived aliasing patterns • Consistent with Nyquist frequency of 60cpd 3.16

17. The L- and M-Cone Mosaic • Foveal mosaic • no S-cones nor rods 3.17

18. The L- and M-Cone Mosaic • Cone receptor mosaic, Roorda and Williams, 1999 • all three type of cones visible, L(red), M(green), S(blue) 3.18