1. Sensation and Perception 19th October 2007 tomesova@ftvs.cuni.cz

2. Information-processing system Sensation: stimulation of receptors - registered in the brain Perception: brain interprets sensations

3. Differences in sensory and perceptual capabilities Among species (dog x men’s range of hearing) Among individuals (taste preferences) Why?  Variations in how sensory systems are structured  Higher order processes

4. Processing information: “bottom-up,” or data driven processing “top-down,” or conceptually driven processing

5. Stimulus The quality of a stimulus (color, musical pitch) The quantity of a stimulus (brightness, loudness)

6. Stimulus detection Sensory threshold Distracting factors:  Background noise  Spontaneous activities of sensory cells  Motivation (costs)  Expectations

7. Stimulus discrimination Weber - Fechner’s law the amount by which a stimulus must be increased to produce a just noticeable difference tends to be a constant proportion of the initial stimulus intensity

8. Sensory adaptation Reduced ability to provide information after prolonged, constant stimulation Why?  Sensitivity to CHANGES

9. Perceiving a complex world Direct perspective: all the information comes from the outer world Constructivist perspective: we must supplement it with additional information stored in memory  schemas

10. Expectations and perceptions Perceptual set Expectations based on schemas

13. Basic perceptual processes Form perception Perceptual constancy Depth perception

14. Form perception Gestalt psychologists (Max Wertheimer, Kurt Koffka, Wolfgang Kohler)  Subjective contours  Rules or principles of perceptual grouping  Overestimation of bottom-up processing

15. Figure and ground Bottom-up and top-down processing

17. Depth perception Binocular disparity Monocular depth cues  Motion parallax  Relative size  Relative closeness to horizon  Linear perspective  Texture gradient  Partial overlap  Light and shadow

24. Disorders of perception Sensory distortions  changes in quality, intensity, spatial form of perception (toxic state, depression, migraine…) Sensory deceptions  Illusions  Hallucinations

25. Hallucinations Perceptions which arise in the absence of any external stimulus (false perception) unwilled - not subject to conscious manipulations same qualities as a real perception perceived as being located in the external world auditory, visual, olfactory, gustatory hypnogogic (visual or auditory) palinopsia (reappearance - Parkinson’s) of bodily sensations (temperature, touch, fluid)

26. Illusions involuntary false perception consequent on a real object in which a transformation of the object takes place distortions of real objects extreme tiredness and emotions  completion (banished by attention)  affective (fear)  pareidolic (shapes in clouds)