SENSATION, PERCEPTION, ATTENTION AND SIGNAL
DETECTION THEORY
Sensation and Perception
Perception involves using prior knowledge to interpret the sensory stimuli
detected by our senses. For example, to read this text, you must:
Register visual information from the page using your eyes
(sensation).
Recognize the shape of letters using knowledge of the alphabet
(perception).
Understand words and sentences using language knowledge
(perception).
Perception relies on both bottom-up sensory input and top-down
influences like expectations, context, and memories.
Visual Object Recognition
Object recognition involves identifying a meaningful pattern of sensory
stimuli as distinct from the background. This requires:
Feature extraction - detecting basic stimulus attributes like edges,
contours, color, movement.
Pattern recognition - relating extracted features to stored object
knowledge to identify and categorize the object.
Parallel processing - features detected simultaneously across visual
field enabling rapid recognition.
Anatomy of the Eye
Key structures involved in vision include:
Sclera/cornea - Outer protective layer with transparent cornea for
light entry.
Iris - Pigmented, controls pupil size to regulate light levels.
Pupil - Variable aperture that controls light entering eye.
Lens - Transparent, focused by ciliary muscles, refracts light onto
retina.
Retina - Inner light-sensitive layer with rod and cone photoreceptors.
Fovea - Central retina area with high acuity/color vision due to dense
cones.
Optic nerve - Exits eye and carries neural signals to brain.
Blind spot - Spot where optic nerve exits lacks photoreceptors.
Aqueous/vitreous humors - Fluids providing shape and nutrition.
Anatomy of the Ear
Key auditory structures include:
Outer ear - Funnels sound waves down ear canal.
Middle ear - Tympanic membrane and ossicles amplify and transmit
vibrations.
Inner ear - Cochlea converts vibrations into neural signals sent to
brain via auditory nerve.
Hair cells - Sensory receptors that detect specific sound frequencies.
Semi-circular canals - Detect head motion and orientation.
Signal Detection Theory
Signal detection theory examines decision-making in perception. Key
principles:
Faint stimuli are detected against background noise.
Subject makes decision if signal is present based on available
evidence.
Decision-making introduces cognitive influences beyond basic
sensory processing.
Accuracy depends on signal strength relative to noise.
Provides framework for analyzing attention, memory and other
cognitive processes.
Attention and Perception
Attention allows selectively processing relevant information. Perception
theories include:
Bottom-up - Builds percepts from sensory features to whole objects.
Top-down - Uses knowledge and expectations to guide
interpretation.
Template matching - Compares stimuli to stored templates.
Feature analysis - Recognizes stimuli by component features.
Recognition-by-components - 3D object recognition using viewpoint-
invariant geons.
