same area of visual space – same region of the brain Οπτικό Πεδίο, 2 μάτια: same area of visual space – same region of the brain S12 Αριστερό ημιπεδίο Δεξιό ημιπεδίο

VISUAL HEMIFIELD ‘monocular crescent’ temporal hemi-retina nasal hemi-retina

VISUAL PATHWAY only nasal fibres cross over optic nerve = ‘decussation’ optic nerve chiasm optic tract lateral geniculate nucleus optic radiation primary visual cortex ‘Meyer’s Loop’

- 90% of the fibers innervate the LGN - the remaining 10% are more than the ones found in the entire auditory pathway - superior colliculus & pulvinar nucleus: play a big role in visual attention - the retino-collicular pathway belongs to a more primitive visual system

- Schneider (1969): V1&V2 lesion or ablation of input fibers to SC in hamsters trained in a localisation and a discrimination task (double dissociation) - “blindsight”: subcortical pathways and/or processing in extrastiate (= beyond V1) cortex?

Rafal et al. 1990: hemianopic patients (V1 lesion) were slower in eye-movement responses (but not in button-presses) when a distractor was presented to the blind hemifield (competing eye-movement signals are generated in the SC that still ‘sees’ the distractor)

lateral geniculate nucleus of the thalamus (LGN)

6 distinct layers receiving monocular input: 4 P(arvocellular) - μικροκυτταρικές στοιβάδες (χρώμα, σχήμα) 2 M(agnocellular) - μεγαλοκυττατικές στοιβάδες (κίνηση)

for a given eccentricity, M-cell receptive fields are 2-3 times larger (i.e. worse spatial resolution) than P-cell receptive fields P pathway: colour, spatial detail (detect changes in spatial (space) domain) M pathway: motion & flicker (detect changes in temporal (time) domain)

equiluminance/isoluminance (M-system ‘blind’?) equiluminant grating: the red and green stripes are of equal luminance, i.e. the grating is defined by colour-contrast alone

The M-system has a high temporal resolution but can only detect luminance-contrast and so the equiluminant stimulus is seen only by the P-system (that can detect colour-contrast) which has a poor temporal resolution (but very good spatial-resolution) and thus leads to an impaired processing (& thus perception) of the motion-information.