Mathematics of Life (9780465024407) by Stewart Ian

Author:Stewart, Ian [Stewart, Ian]
Language: eng
Format: epub
ISBN: 9780465024407
Publisher: Perseus
Published: 2011-04-04T05:00:00+00:00

Fig 42 Left: Archimedean spiral. Right: Logarithmic spiral.

Fig 43 Retino-cortical map.

The most significant feature of this ‘retino-cortical map’ is that it turns logarithmic spirals on the retina into parallel lines in the cortex. The visual system automatically makes us ‘see’ anything detected by the cortex, whether or not it originates in the eye, so we will ‘see’ spirals if something creates a pattern of parallel stripes on the cortex. Psychotropic drugs cause waves of electrical activity, and the simplest wave pattern is stripes.

If the stripes move, forming travelling waves like ocean waves coming up a beach, then the geometry of the retino-cortical map implies that the spirals will appear to rotate. Radial spokes are a special case of spirals, and correspond to horizontal stripes on the cortex (relative to the conventional orientation of the cortex). As the waves travel across the cortex, the spokes rotate. Concentric circles similarly correspond to vertical stripes; this time, as the waves travel across the cortex, the circles appear to expand from their centre (see Figure 44).

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