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Chapter 4

Chapter 4. Sensation and Perception. Sensation and Perception: The Distinction. Sensation : stimulation of sense organs Perception : selection, organization, and interpretation of sensory input Psychophysics = the study of how physical stimuli are translated into psychological experience.

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Chapter 4

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  1. Chapter 4 Sensation and Perception

  2. Sensation and Perception: The Distinction • Sensation : stimulation of sense organs • Perception: selection, organization, and interpretation of sensory input • Psychophysics = the study of how physical stimuli are translated into psychological experience

  3. The distinction between sensation and perception

  4. Psychophysics: Basic Concepts • Sensation begins with a detectable stimulus • Psychological versus physical • Fechner: the concept of the threshold • Absolute threshold: detected 50% of the time. –Just noticeable difference (JND): smallest difference detectable • Weber’s law: size of JND proportional to size of initial stimulus

  5. Psychophysics: Concepts and Issues • Signal-Detection Theory: Sensory processes + decision processes – • Applications • Subliminal Perception: Existence vs. practical effects • 1957 study in a drive in movie • Objective evaluation – critical thinking • Sensory Adaptation: Decline in sensitivity

  6. Vision: The Stimulus • Light = electromagnetic radiation - • Amplitude: perception of brightness • Wavelength: perception of color • purity: mix of wavelengths • perception of saturation, or richness of colors. – • Refraction • Reflection • Absorption • Diffraction

  7. The Eye: Converting Light into Neural Impulses • The eye: housing and channeling • Components: • Cornea: where light enters the eye • Anterior chamber • Lens: focuses the light rays on the retina - presbyopia • Iris: colored ring of muscle, constricts or dilates via amount of light • Pupil: regulates amount of light • Eye conditions – • Nearsightness – mypoia • Farsightness - hyperopia

  8. The human eye

  9. Nearsightedness and farsightedness

  10. The Retina: An Extension of the CNS • Retina: absorbs light, processes images, and sends information to the brain • Optic disk: where the optic nerve leaves the eye/ blind spot • Receptor cells: - • Rods: black and white/ low light vision • Cones: color and daylight vision • Adaptation: becoming more or less sensitive to light as needed – • Information processing: • Receptive fields • Lateral antagonism

  11. The retina

  12. Hubel and Wiesel: Feature Detectors and the Nobel Prize • Early 1960’s: Hubel and Wiesel • Microelectrode recording of axons in primary visual cortex of animals • Discovered feature detectors: neurons that respond selectively to lines, edges, etc. – • Groundbreaking research: Nobel Prize in 1981 • Later research: cells specific to faces in the temporal lobes of monkeys and humans • Cell specialization –– fusifacial form area (FFA) – Quiroga et al. (2005) - hippocampus cells- common name? • Greebles research – Gauthier et al. (1999) – • Facial recognition cells can be trained to recognize other types of stimuli

  13. The Retina and the Brain: Visual Information Processing • Light -> rods and cones -> neural signals -> bipolar cells -> ganglion cells -> optic nerve -> optic chiasm -> opposite half brain -> • Main pathway: lateral geniculate nucleus (thalamus) -> primary visual cortex (occipital lobe) • magnocellular: where • parvocellular: what • Blindsight – Wesiskrantz (1994) • Second pathway: superior colliculus ->thalamus -> primary visual cortex

  14. Figure 4.15 The what and where pathways from the primary visual cortex

  15. Basics of Color Vision • Wavelength determines color • Longer = red / shorter = violet • Amplitude determines brightness • Purity determines saturation • Computer generated colors and human color vision: 48 bit color scanners v. humans

  16. The color solid

  17. Additive versus subtractive color mixing

  18. Theories of Color Vision • Trichromatic theory - Young and Helmholtz • Receptors for red, green, blue – color mixing – • Opponent Process theory – Hering • 3 pairs of antagonistic colors – negative afterimages • red/green, blue/yellow, black/white • Current perspective: both theories necessary • Color vision defects • Color vision defects: simulations

  19. Perception: Perceiving Forms, Patterns, and Objects • Reversible figures – • Perceptual sets – readiness to perceive a stimulus in a particular way – ambiguous stimuli – effects of motivational factors • Inattentional blindness/change blindness – • http://www.youtube.com/watch?v=nkn3wRyb9Bk&feature=related • http://www.youtube.com/watch?v=38XO7ac9eSs • Feature detection theory - bottom-up processing. • Form perception - top-down processing • Subjective contours • Gestalt psychologists: the whole is more than the sum of its parts • Reversible figures and perceptual sets demonstrate that the same visual stimulus can result in very different perceptions

  20. XX4.25

  21. XX4.27

  22. Principles of Perception • Gestalt principles of form perception: • figure-ground, proximity, similarity, continuity, closure, and simplicity • Point of view effects – • Recent research: • Distal (stimuli outside the body) vs. proximal (stimulus energies impinging on sensory receptors) stimuli. • Perceptual hypotheses • Context • Object recognition – object background consistency –

  23. Depth and Distance Perception • Binocular cues – clues from both eyes together • retinal disparity – up to 25 feet • Convergence • Creating 3D effects – stereoscope – after Wheatstone and Viewmasters, random dot stereogram- after Brewester, Red-green anaglyphs, and autostereograms – Magic Eye • strabismus or "wandering eye" – stereoblindness (5 – 10%), the case of “Stereo Sue” • Monocular cues – clues from a single eye – Figure motion parallax • accommodation • pictorial depth cues

  24. Wheatstone's original stereoscope

  25. Schematic of red-green anaglyphs

  26. Random Dot stereograms

  27. Emphasis on linear perspective during the Western Renaissance

  28. Stability in the Perceptual World: Perceptual Constancies • Perceptual constancies – stable perceptions amid changing stimuli • Size • Shape • Brightness • Hue • Location in space

  29. Optical Illusions: The Power of Misleading Cues • Optical Illusions - discrepancy between visual appearance and physical reality • Famous optical illusions: Muller-Lyer Illusion, Ponzo Illusion, Poggendorf Illusion, Upside-Down T Illusion, Zollner Illusion, the Ames Room, and Impossible Figures • Cultural differences: Perceptual hypotheses at work • http://www.michaelbach.de/ot/ - website with visual illusions and other visual effects • Art and Illusion – pages 175 - 179

  30. Hearing: The Auditory System • Stimulus = sound waves (vibrations of molecules traveling in air) • Amplitude (loudness) • Wavelength (pitch) • Purity (timbre) • Wavelengthdescribed in terms of frequency: measured in cycles per second (Hz) • Frequency increase = pitch increase • Sound pressure (SPL) – decibels –

  31. The Ear: Three Divisions • External ear (pinna): collects sound. • Middle ear: the ossicles (hammer, anvil, stirrup) • Inner ear: the cochlea • a fluid-filled, coiled tunnel • contains the hair cells, the auditory receptors • lined up on the basilar membrane

  32. The human ear

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