Vision. The Visible Spectrum. Light is electromagnetic energy. One nm = one billionth of a meter. Properties of light. hue – determined by wavelength. saturation – relative purity of light. brightness – variation in intensity. Wavelength and Frequency.
Light is electromagnetic energy.
One nm = one billionth of a meter
As wavelength increase, frequency decreases
In order to see things in greatest detail our eyes are moved so that the object being looked at falls on the fovea.
Fovea is a central portion of the retina with the greatest visual acuity.
Optic disk – where the optic nerve joins the retina – transmits retinal information to the occipital lobes
Close your LEFT eye and move head closer to or further away from the screen until
the central red circle disappears – always fixate the CROSS.
dorsal lateral geniculate nucleus
striate visual cortex
The LGNd has six layers each of which gets independent input from either the left or the right eye but not both.
There are two major classes of projections, parvocellular (small) and magnocellular (large) projections(known as the P and M pathways).
Small ganglion cells
High contrast sensitivity
Low contrast sensitivity
The LGNd projects to primary visual cortex (striate cortex or area V1) in the occipital lobe.
The magno and parvo projections are still somewhat segregated in V1.
Coding information at the retina - colour specific regions in space – hence a
high spatial because the “green” component of red/green cells has adapted to the
Gender and can still be extracted from the low frequency image (right) but identity requires the high frequency image (left).
Review Questions processes
1) A unique feature of the fovea is that it
A) contains mostly rods.
B) contains mostly cone photoreceptors.
C) is devoid of photoreceptors.
D) mediates vision in dim light.
E) has very poor acuity.
2) The reason for a "blind spot" in the visual field is that
A) rods are less sensitive to light than are cones.
B) blood vessels collect together and enter the eye at the blind spot.
C) the lens cannot focus all of the visual field onto the retina.
D) retinal cells die with age and overuse, resulting in blind spots.
E) there are no photoreceptors in the retina where the axons exit the eye.
A) bipolar cells.
B) horizontal cells.
C) ganglion cells.
E) axons leaving the internal surface of the retina.
4) Select the correct sequence for processing of information in the primary visual pathway.
A) Retina - > dorsal lateral geniculate (DLG) -> striate cortex
B) Retina -> striate cortex -> extrastriate cortex -> inferior temporal cortex
C) DLG -> retina -> striate cortex -> primary visual cortex
D) Retina -> DLG -> inferior temporal cortex -> amygdala
E) DLG-> frontal cortex -> amygdala -> extrastriate cortex
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