PSY 102 Lecture Notes - Lecture 4: Reticular Formation, Gustav Fechner, Detection Theory
11 May 2018
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Chapter 4: Sensation & Perception
1. Sensation & Perception
− Sensation: stimulation of the sense organs (sensation is passively receiving information
through sensory inputs)
o Stimulus (physical energy) is “raw data” about the outside world
o Received by specialized “receptor” cells in eyes ears, skin, nose, tongue etc
o “Raw data” sent to the brain
− Perception: the organization and interpretation of sensations (interpreting this
information)
o Brain makes sense of “raw data”
o Influence by knowledge of the world, expectations, context, etc
o Limited by attention
o Simons & Chabris (1999) found that 73% of participants failed
▪ We focus selectively because mental resources are limited
▪ We make choices about which parts of environment to process more
deeply
➢ Psychophysics (Gustav Fechner called the study of how external stimuli affect us
psychophysics)
▪ Branch of psychology that deals with the relationship between physical
stimuli and psychological experience. (in other words: between mental and
physical process)
▪ Set of methods for quantifying what people are able to detect.
• Absolute threshold (also detection threshold): intensity level at which a person detects
the presence of the stimulus 50% of the time.
Absolute threshold refers to the weakest possible stimulus that a person can still
perceive. e.g.) lowest level of intensity that can be detected
− It is not easy thing to measure
▪ Lapses in attention
▪ Background noise may change slightly
▪ Uncertainty, lying
• Just noticeable difference (JND): smallest difference between .e.g)stimuli that can be
detected.
▪ Can present people with pairs of lights of find JND
− Weber’s law: just noticeable difference’ of a stimulus is proportional to the
original intensity of stimulus.
just noticeable difference …is a constant proportion of the magnitude of the
standard stimulus.
e.g.:)- in a room lit by 5 candles (standard), it takes 1 candle to notice a
difference (1/5 = 20%)
- in a room lit by 10 candles (standard), it takes 2 candles to notice a
difference (2/10 = 20%)
- in a room lit by 100 candles (standard), it takes 20 candles to notice a
difference (20/100 = 20%)
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find more resources at oneclass.com
• Signal detection theory: provides a set of statistical procedures for removing
response bias from threshold estimates.
Role of Attention (attention affect our abilities to sense and perceive)
− selective attention: process of selecting one sensory channel and ignoring or minimizing
others. In order words, when perceiving the world around us, choosing to focus on certain
sensations over others.
− Reticular activating system (RAS) and forebrain involved in selective attention.
− Attention often metaphorically conceived of as a filter. (this mental filter enables us to
pay attention to important stimuli and ignore others.
− Dichotic listening: a technique in which two different auditory messages are presented
simultaneously, one to each ear; usually the subject’s task is to shadow, or repeat loud,
one message while ignoring the other.
2. Seeing: the visual system
− Light: the energy of life
o a light source (e.g. sun, candle, a firefly) emits electromagnetic radiation that
travels as a wave.
o Waves can differ in amplitude (height of the peaks) and wavelength (distance
between peaks).
o Tiny arrange of possible wavelengths is visible as light
o Brightness: subjective perception of amplitude (low amplitude dull, high light)
o Colour or hue: subjective perception of wavelength
The eye: how we represent the visual realm.
Light first passes thorough the cornea, the outermost part of eyeball, where it begins to be
focused. Then it enters the pupil, a small opening that leads to the lens.
− Pupil: regulates amount of light passing into the eye
− Cornea: curved, transparent layer covering the iris and pupil
− Lens: focuses light rays to fall on the retina
o Curvature of the lens adjusts (accommodates) ->closer object =fattens; further
object =flattens. Accommodation is that a surface where it is further focused
through a process.
− retina: tissue lining the inside back of eye that contains the receptors for seeing
o cones: receptors for daylight, fine detail, and colour vision and image details.
o rods: receptors for night and peripheral vision (white and black).
▪ Color-blindness would be missing the cones.
o stimulation of roads and cones converted to neural impulses that are sent to the
brain via the optic nerve
o after visual cortex, further processing along dorsal and ventral pathways.
▪ Dorsal stream: where->action pathway
▪ Ventral stream: what ->perception pathway
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 4: sensation & perception: sensation & perception. Absolute threshold refers to the weakest possible stimulus that a person can still perceive. e. g. ) lowest level of intensity that can be detected. In a room lit by 10 candles (standard), it takes 2 candles to notice a difference (2/10 = 20%) In a room lit by 100 candles (standard), it takes 20 candles to notice a difference (20/100 = 20%) Signal detection theory: provides a set of statistical procedures for removing response bias from threshold estimates. Role of attention (attention affect our abilities to sense and perceive) Selective attention: process of selecting one sensory channel and ignoring or minimizing others. In order words, when perceiving the world around us, choosing to focus on certain sensations over others. Reticular activating system (ras) and forebrain involved in selective attention. Attention often metaphorically conceived of as a filter. (this mental filter enables us to pay attention to important stimuli and ignore others.
