PSY 100 - Chap 4 Sensation and Perception
-the registration of sensory input without conscious awareness
-perception without awareness can take place
- a gradual decline in sensitivity due to prolonged stimulation
-another factor that influences registration of sensory input
-an automatic, built-in process that keeps people tuned into the changes rather than the
constants in their sensory input
-a form of electromagnetic radiation that travels as a wave, moving, naturally enough, at
the speed of light
-amplitude: affects the perception of brightness
-wavelength: affects the perception of color
-purity: influences perception of the saturation, or richness, of colors
-retina: neural tissue lining the inside back surface of the eye; it absorbs light,
processes images, sends visual info to the brain; the axons run from the retina to the
brain converge at the optic disk.
-optic disk: a hole in the retina where the optic nerve fibres exit the eye; part of an
image cant be seen “blind spot”
-cornea: a transparent “window” at the front that light enters into the eye.
-lens: locate behind cornea , form an upside-down image of objects with cornea on the
retina; focuses the light rays falling on the retina; made up of soft tissue, capable of
adjustments that facilitate a accommodation process (curvature of the lens adjusts to
alter visual focus).
-nearsightedness: focus point falls in front of retina; eyeball is too long.
-farsightedness: focus point falls behind retina; eyeball is too short
-iris: the colored ring of muscle surrounding the pupil.
-pupil: the opening in the centre of the iris that helps regulate the amont of light passing
into the rear chamber of the eye; constricts = less light = sharpens image; dilates =
more light = less sharp
-saccades: eye movements
-10% of the light arriving at the cornea reaches receptors.
-2 type of receptors: rods & cones ; rods outnumber cones by huge margin, (100M
-125M rods vs. 5M - 6.4M cones)
-cones: specialized visual receptors that play a key role in daylight vision and colour
vision; do not respond well to dim light; provide better visual acuity (sharpness and
precise detail) than rods; concentrated most heavily in the centre of the retina and fall off
in density toward its periphery.
-fovea: a tiny spot in the centre of the retina that contains only cones; visual acuity is
the greatest at this spot.
-rods: specialized visual receptors that play a key role in night vision and peripheral
vision; more sensitive to dim light; outnumber cones in the periphery of the retina;
density is greatest outside the fovea and gradually decreases toward the periphery of
the retina; adverted vision for dark objects.
-dark adaptation: the process in which the eyes become more sensitive to light in low
illumination; complete in 30 mins.
-light adaptation: the process whereby the eyes become less sensitive to light in high
illumination. improves visual acuity
-receptive field: made up of rods and cones in the retinal area, when stimulated, affects
the firing of the visual cell.
-lateral antagonism: occurs when neural activity in a cell opposes activity in
Vision and the brain
-optic chiasm- the point at which the optic nerves from the inside half of each eye cross
over and project to the opposite half of the brain
-axons from the left half of each retina carry signals to the left side of the brain, vice
-after meeting the optic chiasm, the optic nerve fibres diverge 2 pathways, the main
pathway projects into the thalamus (brain’s major replay station); the second visual
pathway leaving the optic chiasm branches off to superior colliculus (midbrain);
function of 2nd pathway is the coordination of visual input with other sensory input.
-90% of the axons from the retinas synapse in the lateral geniculate nucleus (LGN);
visual signals are processed in the LGN and distributed to areas in the occipital lobe that
make up the primary visual cortex.
-Main visual pathway is subdivided into: magnocellular (processes info regarding
brightness) and parvocellular (handles perception of color) channels. they engage in
parallel processing, which involves simultaneously extracting different kinds of info from
the same input.
-simple cells respond best to a line of the correct width, oriented at the correct angle,
and located in the correct position in its receptive field.
-complex cells more responsive if a line sweeps across their receptive field, only if it
moves in the right direction.
-feature detectors: neurons that respond selectively to very specific features of more
-after visual input is processed in the primary visual cortex, it travels through 2 streams:
ventral stream (processes the details of what objects are out there, perception of form
and color of the external world); dorsal stream (processes where the objects are,
perception of motion and depth; visual control of action)
-brain can be rewired by experience.
-McCollough effect: a well-known afterimage phenomenon that is contingent on both
colors and patter/form.
-visual agnosia: an inability to recognize familiar objects.
Review of Key Points:
-light varies in terms of wavelength, amplitude, and purity. light enters the eye through
the cornea and pupil and is focused upside down on the retina by the lens. distant
objects appear blurry to nearsighted people and close objects appear blurry to
-the retina is the neural tissue in the eye that absorbs light, processes images, and
sends visual signals to the brain. cones, which are concentrated in the fovea, play a key
role in daylight vision and color perception. rods, which have their greatest density just
outside the fovea, are critical to night vision and peripheral vision. dark adaptation and
light adaptation both involve changes in the retina’s sensitivity to light, allowing the eye
to adapt to changes in illumination.
-the retina transforms light into neural impulses that are sent to the brain via the optic
nerve. receptive fields are areas in the retina that affect the firing of visual cells. they
vary in shape and size, but centre-surround arrangements are common. the optic
nerves from the inside half of each eye cross at the optic chiasm and then project to the
opposite half of the brain.
-two visual pathways engage in parallel processing and send signals to different areas
of the primary visual cortex. the main pathway is routed through the LGN in the
thalamus. after processing in the primary visual cortex, visual info is shuttled along the
what and where pathways to other cortical areas.
-nobel prize- winning research by Hubel and Wiesel suggests that the visual cortex
contains cells that function as feature detectors. the discovery of the what pathway and
the neurons inside it that respond specifically to faces have shed new light on visual
disorders that have perplexed scientists for decades.
-vision researchers employ multiple, converging methods when trying to explain the role
of the brain in visual experience. this was illustrated with recent research on the
The stimulus for color
-wavelength = hue , amplitude = brightness, purity = saturation
-subtractive color mixing - removing some wavelengths of light, leaving less light than
was originally there.
-additive color mixing - superimposing lights, putting more light in the mixture than
exists in any one light by itself.
Psy 100 - chap 4 sensation and perception subliminal perception the registration of sensory input without conscious awareness. Perception without awareness can take place sensory adaptation. A gradual decline in sensitivity due to prolonged stimulation. Another factor that influences registration of sensory input. An automatic, built-in process that keeps people tuned into the changes rather than the constants in their sensory input. A form of electromagnetic radiation that travels as a wave, moving, naturally enough, at the speed of light. Purity: influences perception of the saturation, or richness, of colors. Eye retina: neural tissue lining the inside back surface of the eye; it absorbs light, processes images, sends visual info to the brain; the axons run from the retina to the brain converge at the optic disk. Optic disk: a hole in the retina where the optic nerve fibres exit the eye; part of an image cant be seen blind spot .