Week 4 Flashcards
Fovea
The area of high resolution, full colour vision, or fovea, is only 1.5 deg across, and the highest receptor density in the fovea only is 20 minutes of arc ( = 0.33 deg).
Rods
Nearly cylindrical
90-95% of human retina
greatest incidence in species that are active at night
located (or most active?)toward the periphery
no direct contribution to colour vision
strong response to dim light
little contribution to perception in detail
Cones
Tapered at one end
5-10% prevlance in human retina
Greatest incidence in birds, primates and other species that are active during the day
Area located mostly in (or is it mostly active in:?) = the fovea
CRITICAL FOR COLOUR VISION
response to dim light is weak
contribute MUCH to perception in detail
Blue Cones
Maximally response to light with wavelngth of 430nm
Rods maximally active
~ 450 to 495nm
Green cones
maximally active ~ 530nm
Red cones
maximally active ~560nm
Spectral sensitivity functions for rods and the three types of cones
Figure 5.14 Spectral sensitivity functions for rods and the three types of cones. The short-wavelength (“blue”) cones are maximally responsive to light with a wavelength of 430 nm. The peak sensitivities of the medium-wavelength (“green”) and long-wavelength (“red”) cones are shifted to longer wavelengths. White light such as daylight activates all three receptors because it contains all wavelengths.
cerebral achromatopsia
Patients with the rare condition of
cerebral achromatopsia
cannot perceive colors, due to damage of
cortex in the inferior temporal lobe of both cerebral hemispheres
Lateral Geniculate Nucleus and Cortex
The primary visual pathway in simians. This is also called the retinogeniculostriate path way
Eye/Retina > Optic Nerve > optic Chiasm > optic tract > Lateral Geniculate nucleus > optic radiations (into V1) >priimary visual cortex (v1)
another visual pathway that is used for detection of fast moving objects in the peripheral visual field
There is another visual pathway that is used for detection of fast moving objects in the peripheral visual field that drive oriented eye and head movements – it involves the superior colliculus. We will find out later that it is also involved in rapid emotional responses to visual objects.
Eye > superior colliculous > pulvinar > (amgydla) Other visual cortical areas (v1 etc)
Contralaterlism
Information from the right side of each retina goes to the right Lateral geniculate nucleus
Information from the contralateral side goes to layesr 1,4 and 6
information from the ipsilateral side goes to layers 2, 3 and 5
Layers 5 and 6 receive inpurt from the magnocellualr pathway
layers from 1-4 receive input from the parvocellular pathway
(flipped for left side of each retina?)
The two pathways
Magnoceullar path
Parvocelluarl path
The two types of pathways
convey different types of
visual information to higher
order visual areas
Summary of the prominent visual areas and the pattern of connectivity in the macaque.
Whereas all cortical processing begins in V1, there are two processing streams that extend either dorsally to the parietal lobe or ventrally to the temporal lobe. The stimulus required to produce optimal activation of a cell becomes more complex along the ventral stream. In addition, the size of the receptive fields of these cells increases, ranging from the 0.5-degree span of a V1 cell to the 40-degree span of a cell in area TEO (temporal occipital).
Summary of what the two pathways can do
Recognition: (What pway)
starts at V1 up to v2 to v3 (dynamic form) and v4 (colour form) then on to Temporal visual areas
Action (where pathway)
V1 to V5 (motion) and V3a (form) on to Parietal Visual Areas