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Lecture 4

PSYCH 111 Lecture 4: Sensation and PerceptionPremium

4 pages58 viewsWinter 2019

Department
Psychology
Course Code
PSYCH 111
Professor
Shelly Schreier
Lecture
4

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Lecture 4:
Sensation – stimulus deception process, sense organs respond to/translate stimuli
into nerve impulses sent to brain
Perception – active process of organizing stimulus input/giving it meaning
Stimulus detection – stimulus intensity needed for us to recognize its presence
Absolute threshold – lowest intensity which stimulus can be detected at least 50%
of time
o Vision – candle flame @ 30 miles on a clear night
o Hearing – watch ticking @ 20 ft in a quiet room
o Taste – 1 tsp sugar in of H20
o Smell – 1 drop perfume in 6(or 3) room apt
o Touch – wing of fly on cheek dropped from 1 cm
Just noticeable difference – minimum in change in stimulus that can be detected
Weber’s Law – difference in threshold directly proportional to magnitude of
stimulus to which comparison is being made
o Value for weight is 2-3%
o Backpack example – heavier compared to original weight (noticeable or
not)
Fechner’s Law – larger increases in physical energy required to produce equal
increases in perception
o Light bulb example – need more energy to perceive an equal difference
Signal detection theory – various factors influence sensory judgement
o Involves decision process in addition to sensation
o Scary movie example – amplified senses
Sensory adaptation (habituation) – over time neurons decrease activity in response
to constant stimulus
o Pay less attention to it over time
Sensory Systems – Vision:
Normal stimulus for vision is electromagnetic energy/light waves
Light waves measured in nanometers
Visual system sensitive to wavelengths extending from ~700 nm (red) to ~400 nm
(blue-violet)
ROY G BIV – higher to lower wave lengths
Human Eye
o Light waves enter eye through cornea
o Pupil – behind cornea, adjusts to control amount of light entering eye
o Iris – pupil size controlled by muscles in colored iris surrounding pupil
o Low light levels cause pupils to dilate – allows more light/improves
optical clarity
o Lens – behind pupil – thinner for distant objects, thicker for nearby objects
o Lens focuses images onto retina, reverses image from right to left/top to
bottom
§ Brain reconstructs it into image we perceive
o Retina – contains specialized sensory neurons
o Optic disk – hole in retina yielding blind spot
§ We don’t experience – each eye compensates for blind spot of
other
o Retina contains 2 types of light sensitive receptor cells (rods and cones)
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