Distinguishing Reality from Illusion

1. Distinguishing Reality from Illusion Visual sensation and perception: A model for the other sensory systems

2. Common Properties of the Senses • Gather and amplify stimulus energy • The distal stimulus (anything outside the body) • The proximal stimulus (receptors inside the body) • Transduction • Receptors transform physical stimulus energy into electrical signals • Sensory coding • “Translation” of stimulus information into dimensions of sensation and perception (e.g., intensity: less vs. more bitter; quality: sweet vs. sour) • Interaction between sensory system and other parts of the system (e.g., adaptation of taste), in time (past vs. present) and/or space (one region vs. another)

3. Sensation and Perception: The Distinction • Sensation (“bottom-up” processing) • Stimulation of sense organs • Perception (“top-down” processing) • Selection, organization, and interpretation of sensory input

4. Vision:The Stimulus…“Gathering in” • Light = electromagnetic radiation • Amplitude: “Amplification…interaction” the perception of brightness • Wavelength: perception of color • Purity: mix of wavelengths • perception of saturation, or richness of colors

5. (Based on Figure 4.2, Weiten)

6. The Eye: A Living Optical Instrumentwhere “Transduction” begins “Sizes” Pupil Pupil Regulates light Focuses Light enters

7. The Retina: The Brain’s Envoy in the Eye • Retina: “Transduction” • Optic disk • Receptor cells: “Transduction” • Rods • Cones • Adaptation: “Interaction”

8. “Interaction” Figure 4.5, Weiten Cones are more sensitive here Rods are more sensitive here

9. Light 1: rods & cones • Bipolar, ganglion cells 3. Optic nerve 4. Optic chiasm

10. Theories of Color Vision • Trichromatic theory: Young and Helmholtz • Opponent Process theory: Hering • antagonistic colors: red/green, blue/yellow, black/white • Current perspective: both theories necessary

12. Figure 4.15, Weiten

13. Perceiving Forms, Patterns, and Objects • Feature analysis • Reversible figures and perceptual sets (Top-down) • Gestalt psychologists: “the whole is different from the sum of its parts”

14. Figure 4.17, Weiten Bottom-up processing

15. Figure 4.8, Weiten • Bottom-up processing: 1960’s: Hubel and Wiesel • Primary visual cortex of cats: Major cell types, visual cortex: Feature Detectors

16. Gestalt Principles of Visual Organization • Figure-ground, proximity, similarity, continuity, closure, and simplicity • Perceptual hypotheses • Context: an example • Induced Motion

17. Closure Poggendorf Illusion Example The images are exactly the same except for the thick black area in the right image (an example of the Poggendorf illusion (1860)). In the figure on the right, there appear to be two continuous diagonal lines: a red and a blue line. What occurs in your visual system that could account for the appearance of the continuous diagonal lines?

18. Closure leads to subjective contours Kaniza Figures

19. Figure/ground (explains reversible figures) Escher

20. Figure 4.24, Weiten

21. Perceiving Depth and Distance • Binocular cues – clues from both eyes together • retinal disparity • convergence • Monocular cues – clues from a single eye • accommodation • pictorial depth cues

23. Perceiving Depth and Distance • Binocular cues – clues from both eyes together • retinal disparity • convergence • Monocular cues – clues from a single eye • accommodation • pictorial depth cues • Thus: an interaction of physiological and experience

24. Perceptual Constancies in Vision • Perceptual constancies – stable perceptions with changing stimuli • Size • Shape • Brightness • Hue • Location in space

26. The Power of Misleading Cues: Optical Illusions • Optical Illusions: discrepancy between visual appearance and physical reality. • Famous optical illusions: Muller-Lyer Illusion, Ponzo Illusion, impossible figures, and the moon illusion.

27. Figure 4.27 The Müller-Lyer illusion. Go ahead, measure them: the two vertical lines are of equal length.

28. Figure 4.28, Weiten