A virtual reality? Human
perceptual function
R.Fielding
Community Medicine & BSU
HKU
Lecture outline
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Learning objectives
Sensation versus perception
Features of perception
Stimulus characteristics
organizational aspects
Hypothesis testing
Depth perception & cues
Perceptual development
Learning objectives
• differentiate between sensation
and perception.
• describe key functional features of
human perceptual system.
• list stimulus characteristics
commanding attention and
describe organizational aspects of
stimulus processing.
• define and give reasons for
importance of illusions and
hypotheses-testing features of
perception.
• give examples of visual cues in
depth perception.
• Describe the main stages of
perceptual development.
Sensation vs. perception
• Sensation
–Sense organs are energy
detectors and signalling devices,
which give rise to
–afferent neural activity.
–afferent activity presents centrally
primarily as sensation.
Perceptions :
–are synthetic central processes
involving the attribution of
meaning to extrinsic and intrinsic
activity.
–are rule bound hypotheses
applied to anticipated stimuli.
–have “bottom-up” and “topdown” features.
Functional features
• Recognition
–Attentional processes
–Limited capacity channels
–Bottom-up processing (input
driven e.g. detection of specific
elements and assembly into
complex forms e.g. geons*).
–Top-down processing
(knowledge driven, e.g.
contexts and expectations)
–Constancies
• Synthesis
–Top-down processing
–Hypothesis-testing
Stimulus characteristics
• Size, colour, shape, location,
pitch, timbre.
• intensity (brightness/volume)
• magnitude (size)
• contrast
• novelty
• salience (relevance)
Organizational aspects
• Stimuli are provisionally
organized (pre-attentively)
according to bottom-up
processes
–feature analysis; proximity;
organization; similarity;
simplicity; continuity.
Hypothesis testing
• Figure-ground
• perceptual patterning
• illusions
These illustrate the dynamic nature of
perception - i.e. perception is not just
passive reception of sensation but
an active process of constructed
experience based on hypotheses
Depth perception and cues
• Monocular cues
–interposition; relative size;
height in plane; linear
perspective; texture gradient;
light and shadow.
• Binocular cues
–parallax; ocular convergence
Perceptual development
• Is perception innate or learned?
– Birth: visual acuity low: vision directed
at contrast boundaries.
– by 3/12 facial expression detectable.
– by 6/12 acuity good, 1-5 years =adult.
– ~6/12 constancies and self/non-self
• Critical periods for visual
development
• Perceptual-motor (p-m)
coordination intimately linked to
stimulation and active interaction
with environment.
• New p-m learning rapid even in
adulthood if self-generated activity
allowed, but not if inactive.
Relevance to medical care
• Perceptions of threat, vulnerability, risk
• Perceptions of patients by doctors and or
doctors by patients
• Preparation for medical procedures
• Pain and pain control, neurological topics
• Diagnostic skill and error
• Paediatrics, geriatrics, intensive care
• Examinations
• and every other aspect of medical
practice...
Further information
• Atkinson RL, et al. (1993) Introduction to
Psychology (11th Edn.) Ch.5, p. 164-201. or
• Weiten W. (1992) Psychology: Themes and
variations. Ch 4. 107-151.
• Weinman J. (1997) An outline of psychology
as applied to medicine. Ch 2.
• Http://www.bhs.mq.edu.au/psy/105/lectures
– Lectures on Feature Detector and visual
illusions & constancies.