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Sensation and Perception: Understanding the Basics

This chapter explores the fundamental concepts in sensation and perception, including the distinction between the two, psychophysics, visual stimuli, the eye and retina, color vision, and perception of forms and patterns.

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Sensation and Perception: Understanding the Basics

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  1. Chapter 4 Sensation and Perception – 8th Edition

  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. Figure 4.1 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. – F 4.2 • 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 – F 4.3 • 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 - F 4.5 • Amplitude: perception of brightness • Wavelength: perception of color • purity: mix of wavelengths • perception of saturation, or richness of colors. – F 4.6 • 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 – F 4.8 • Nearsightness – mypoia • Farsightness - hyperopia

  8. Figure 4.7 The human eye

  9. Figure 4.8 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: - F 4.8 • Rods: black and white/ low light vision • Cones: color and daylight vision • Adaptation: becoming more or less sensitive to light as needed – F 4.10 • Information processing: • Receptive fields • Lateral antagonism

  11. Figure 4.9 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. – F 4.14 • Groundbreaking research: Nobel Prize in 1981 • Later research: cells specific to faces in the temporal lobes of monkeys and humans • Cell specialization – F 4.16 – fusifacial form area (FFA) – Quiroga et al. (2005) - hippocampus cells- common name? • Greebles research – Gauthier et al. (1999) – F 4.17 • 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. Figure 4.18 The color solid

  17. Figure 4.19 Additive versus subtractive color mixing

  18. Theories of Color Vision • Trichromatic theory - Young and Helmholtz • Receptors for red, green, blue – color mixing – F 4.21 • 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

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  21. Perception: Perceiving Forms, Patterns, and Objects • Reversible figures – F 4.23, F 4.31 • Perceptual sets – readiness to perceive a stimulus in a particular way – ambiguous stimuli – F 4.24 – 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

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  24. Principles of Perception • Gestalt principles of form perception: • figure-ground, proximity, similarity, continuity, closure, and simplicity • Point of view effects – F 4.34 • Recent research: • Distal (stimuli outside the body) vs. proximal (stimulus energies impinging on sensory receptors) stimuli. • Perceptual hypotheses • Context • Object recognition – object background consistency – F 4.35

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  30. 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 4.36 • motion parallax • accommodation • pictorial depth cues

  31. Wheatstone's original stereoscope

  32. Schematic of red-green anaglyphs

  33. Random Dot stereograms

  34. Emphasis on linear perspective during the Western Renaissance

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

  36. 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

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  41. 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 – F 4.48

  42. XXX 4.47

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