1. A virtual reality? Human perceptual function R.Fielding Community Medicine & BSU HKU

2. Lecture outline • Learning objectives • Sensation versus perception • Features of perception • Stimulus characteristics • organizational aspects • Hypothesis testing • Depth perception & cues • Perceptual development

3. 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.

4. 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.

5. 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.

6. 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 “top-down” features.

7. 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*).

8. Top-down processing (knowledge driven, e.g. contexts and expectations) • Constancies • Synthesis • Top-down processing • Hypothesis-testing

9. Stimulus characteristics • Size, colour, shape, location, pitch, timbre. • intensity (brightness/volume) • magnitude (size) • contrast • novelty • salience (relevance)

10. Organizational aspects • Stimuli are provisionally organized (pre-attentively) according to bottom-up processes • feature analysis; proximity; organization; similarity; simplicity; continuity.

11. 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

12. Depth perception and cues • Monocular cues • interposition; relative size; height in plane; linear perspective; texture gradient; light and shadow. • Binocular cues • parallax; ocular convergence

13. 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

14. 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.

15. 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...

16. 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.