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Livingstone and Hubel (1988)

“Human perceptual experiments are remarkably consistent with these predictions”
(from anatomical and physiological observations on the visual system in monkeys)

They review the magno and parvo cells in the LGN. Magno cells have larger receptive fields by a factor of 2 or 3, and magno are much more sensitive to low- contrast stimuli. There are 4 major differences — Colour, acuity, speed, and contrast sensitivity – in LGN

Good review of differences in V1 and V2

Human perception (p744)

“Segregation begun in the eye gives rise to separate and independent parallel pathways

  1. People can follow brightness alternations at much faster rates than pure colour alternations. (Ives, 1923) (Magno is colour-blind and faster)
  2. Perception of movement reflects magno characteristics: colour blindness quickness, high contrast sensitivity and lack of acuity.
    For rotating gratings the sensation of movement is lost at high spatial frequencies
    For moving red and green stripes, the movement stops when the stripes are made equiluminant. In both these the stripes can still be seen in different positions.
  3. Movement can be vividly perceived with very rapidly alternating or low contrast images.
  4. Also stereopsis fails with equiluminant colours and for high, but resolvable spatial frequencies
    lThe ability to use relative motion as a depth cue is lost with equiluminant colours
  5. Depth from shadows depend on contrast, not colour - shadows on Van Gogh’s self portrait are green but convey normal shape.
  6. Depth from perspective fails with equiluminance
    Illusory borders disappear with equiluminance.
  7. Gestalt-type linking by collinearity (e.g. phantom contours) fails with equiluminance
  8. Colours may “bleed” into surrounding grays because the acuity for colour patches is less than the acuity for contours.

Functions

Magno system may have a global function of interpreting spatial organization. But it is no good for sustained scrutiny of detail: this is what the parvo system is for. (p.748)

Psychological evidence from Livingstone 1988

Many visual illusions related to depth perception (Muller-Lyer, Ponzo, and Poggendorff) also disappear with equiluminant colours. (Livingstone and Hubel, 1987)

(Poggendorff is a slanted line through a vertical rectangle (even if this is in “subjective contours — Ponzo is the railway track)


Start | basic neuroanat. | reading | zeki extracts | table of links | List of Refs | Journals