PSYC 200 Lecture Notes - Lecture 4: Photoreceptor Cell, Visual Acuity, Electromagnetic Spectrum
14 Jun 2018
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PSYC Sensation& Perception Chapter 4
Sensation VS Perception
• Sensation: The process of detecting physical energies with the sensory organs.
o Sensory organs react to the world around us.
• Perception: The mental process of organizing sensations into meaningful patterns.
o Our perceptual system interprets information from our senses
Vision – Catching Some Rays
• Visible Spectrum: That part of the electromagnetic spectrum
to which the eyes are sensitive.
• Hue: Classification of colours into basic categories of red,
orange, yellow, green, blue, indigo, and violet.
Structure of the Eye
• Lens: Structure in the eye that focuses light rays.
• Photoreceptors: Cells that are sensitive to light in the retina
• Retina: The layer of photoreceptive cells at the back of the eye.
• Cornea: Transparent membrane covering the front of the eye
• Cornea → Lens → Retina (of photoreceptors) → Optic Nerve
Vision Problems
• Hyperopia (eye is short): Difficulty focusing nearby objects (farsightedness).
• Myopia (eye is elongated): Difficulty focusing distant objects (nearsightedness).
• Astigmatism: Defects in the structure (cornea, lens, or eye) that cause some areas of
vision to be out of focus
o Can be fixed by eyeglasses
• Presbyopia: Farsightedness caused by aging (lens is less flexible; eye is not short)
Video: Ben blind but able to see using sound/echolocation –vibrations bouncing off and seeing
where things are by sounds
• Sense of hearing overcompensating for loss of vision
Rods & Cones
• Visual process starts when light hits the cones/rods.
• Rods (100 million): Visual receptors that produce only black and white sensations.
o HIGHLY sensitive, even in dim light
• Cones (6.5 million): Visual receptors for colours and daylight visual acuity.
o Cones require more light to activate than rods do → more visual acuity/details
• Blind Spot: An area of the retina LACKING visual receptors.
o The retia has a hole here eural ipulses are set through the opti ere.
o Dot eperiee lid spot as rai akes up for it
find more resources at oneclass.com
find more resources at oneclass.com
RODS
CONES
#: 100 million
#: 6.5 million
Sensitive to movement
Visual Acuity
Black & White
Colours
Periphery
Fovea
Visual Activity
• Visual Acuity: The SHARPNESS of visual perception.
• Fovea: An area at the center of the retina containing ONLY CONES
o Produce the sharpest image
Peripheral Vision
• Peripheral Vision: Vision at the EDGES of the visual field
o Mostly have RODS – although they are not sharp, they are sensitive to
movement
Colour Vision - 2 Theories
• (1) Trichromatic Theory: Theory of colour vision based on three cone types: red, green,
and blue
• (2) Opponent-Process Theory: Theory of colour vision based
on three coding systems (red or green, yellow or blue, black or white)
o Cat see reddish-gree at oie fro /i
• Afterimages: Visual sensation that persists after a stimulus is removed
o When looking @ colour for long time (red), then looked away, you would then
see the corresponding colour (green)
Colour Blindness
• Colour Blindness: A total inability to perceive colours.
o Newborns have essentially no colour vision (until 6 months old)
• Colour Weakness: – An inability to distinguish some colours
• Ishihara Test: Test for colour blindness and colour weakness.
o Need to see contrast b/w colours to indicate the #s
Dark Adaptation
: Increased retinal sensitivity to light after entering the dark; similar to going from
daylight into a dark movie theatre → eyes are adapting
Hearing
• Sound Waves: Rhythmic movement of air molecule
2 Properties
o Pitch: Higher or lower tone of a sound; related to the frequency of sound waves
o Loudness: Sound intensity; determined by the amplitude of sound wave
find more resources at oneclass.com
find more resources at oneclass.com
How We Hear Sounds
Outside Ear
• Pinna: External part of the ear
• Tympanic Membrane: Eardrum
• Auditory Ossicles: Three small bones that vibrate; link eardrum with cochlea
o Malleus/hammer
o Incus/anvil
o Stapes/stirrup
• Cochlea: Snail-shaped organ that makes up inner ear. (then vibrates)
Inside Ear
• Hair Cells: Receptor cells within cochlea that transduce (changes signal from vibrations
into nerve impulses)
o Once dead they are NEVER replaced (hearing issues)
o Message transduced → auditory nerve → brain
2 Theories of how pitch is transduced @ cochlea
• Frequency Theory: As pitch rises, nerve impulses of the same frequency are fed into the
auditory nerve (e.g. 800 hertz tone produces 800 impulses/sec)
• Place Theory: Higher and lower tones excite specific areas of the cochlea
o Lower tones = excites higher areas (and vice versa)
• Decibels
o Normal sounds → not dangerous
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Vision catching some rays: visible spectrum: that part of the electromagnetic spectrum to which the eyes are sensitive, hue: classification of colours into basic categories of red, orange, yellow, green, blue, indigo, and violet. Video: ben blind but able to see using sound/echolocation vibrations bouncing off and seeing where things are by sounds: sense of hearing overcompensating for loss of vision. Visual activity: visual acuity: the sharpness of visual perception, fovea: an area at the center of the retina containing only cones, produce the sharpest image. Peripheral vision: peripheral vision: vision at the edges of the visual field, mostly have rods although they are not sharp, they are sensitive to movement. Colour blindness: colour blindness: a total inability to perceive colours, newborns have essentially no colour vision (until 6 months old, colour weakness: an inability to distinguish some colours. Ishihara test: test for colour blindness and colour weakness: need to see contrast b/w colours to indicate the #s.
