PSYC 1020H Chapter Notes - Chapter 4: Visual Cortex, Color Vision, Peripheral Vision
3 May 2018
School
Department
Course
Professor
Sensation And Perception
Psychophysics: Basic Concepts and Issues
● Early work in psychophysics established the existence of two types of sensory
thresholds
○ Absolute threshold: is the smallest level of energy required by an external
stimulus to be detectable by the human senses, including vision, hearing,
taste, smell and touch.
○ Change threshold
● According to signal-detection theory, the detection of sensory inputs is influenced
by noise in the system and by decision-making strategies. In recent years, it has
become apparent that perception can occur without awareness. Prolonged
stimulation may lead to sensory adaptation.
Our Sense of Sight: The visual System
● Light varies in terms of wavelength, amplitude, and purity. Light enters the eye
through the cornea and pupil and is focused on the retina by the lens. Rods and
cones are the visual receptors found in the retina. Cones play a key role in
daylight vision and colour perception, and rods are critical to night vision and
peripheral vision. Dark and light adaptation both involve changes in the retina’s
sensitivity to light.
● 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. Two visual pathways, which engage in parallel processing, send signals
through the thalamus to the primary visual cortex. From there, visual signals are
shuttled along pathways that have been characterized as the what and where
pathways
● Perceptions of colour (hue) are primarily a function of light wavelength, while
amplitude affects brightness and purity and affects saturation. Perceptions of
many varied colours depend on processes that resemble additive colour mixing.
The evidence now suggests that both the trichromatic and opponent process
theories are necessary to account for colour vision.
● Form perception depends on the selection and interpretation of visual inputs.
According to feature analysis theories, people detect specific elements in stimuli
and build them into forms through bottom-up processing. However,evidence
suggests that form perception also involves top-down processing.
● Gestalt psychology emphasized that the whole may be greater than the sum of
its parts (features), as illustrated by Gestalt principles of form perception. Other
Document Summary
Early work in psychophysics established the existence of two types of sensory thresholds. Absolute threshold: is the smallest level of energy required by an external stimulus to be detectable by the human senses, including vision, hearing, taste, smell and touch. According to signal-detection theory, the detection of sensory inputs is influenced by noise in the system and by decision-making strategies. In recent years, it has become apparent that perception can occur without awareness. Light varies in terms of wavelength, amplitude, and purity. Light enters the eye through the cornea and pupil and is focused on the retina by the lens. Rods and cones are the visual receptors found in the retina. Cones play a key role in daylight vision and colour perception, and rods are critical to night vision and peripheral vision. Dark and light adaptation both involve changes in the retina"s sensitivity to light.
