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Chapter 4

Chapter 4 - Sensation and Perception.docx

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PSYC 1010
Jennifer Steeves

Sensation and Perception The Visual System Light Waves Vary in: • Amplitude which affects brightness • Wavelength which affects colour (hue) • Purity which affects saturation Registered by receptors in the eye Key Eye Structures • Lens – focuses the light rays falling on the retina • Pupil – regulates the amount of light passing to the rear of the eye • Retina – the neural tissue lining the inside back surface of the eye • Optic Disk – a hole in the retina that corresponds to the blind spot • Fovea – a tiny spot in the centre of the retina where visual acuity is greatest Visual receptors (in the retina) • Organized into receptive fields • Rods play a key role in night and peripheral vision and greatly out-number cones • Cones play a key role in day colour vision and provide greater acuity than rods • Receptive Fields are collections of rods and cones that funnel signals to specific visual cells in the retina or the brain Visual signals are sent onward to the brain Visual pathways and processing • Main visual pathway – engage in parallel processing of stimulus input  Parvocellular channel  Magnocellular channel • Second visual pathway – handles coordination of visual input with other sensory input • Primary visual cortex – handles the initial cortical processing of visual input (in occipital lobe) • Feature detectors – neurons in the visual cortex that respond selectively o specific features of complex stimuli • After processing in the primary visual cortex, visual input is routed to other cortical areas along the where pathway (dorsal stream) and the what pathway (ventral stream) Optical Illusions • Discrepancy between the appearance of a visual stimulus and its physical reality • The Müller-Lyer illusion, the Ponzo illusion, and the moon illusion, show that perceptual hypotheses can be wrong and that perception is not a simple reflection of objective reality Colour Perception • Subtractive colour mixing works by removing some wavelengths of light, leaving less light • Additive colour mixing woks by putting more light in the mixture than any one light • Trichromatic theory – the eye has 3 groups of receptors sensitive to wavelengths associated with red, green, and blue • Opponent process theory - receptors make antagonistic responses to three pairs of colours • Conclusion – the evidence suggests that both these theories are necessary to explain colour perception Form Perception • The same visual input can result in very different perceptions • Form perception is selective, as the phenomenon of inattentional blindness demonstrates • Some aspects of form perception depend on feature analysis, which involves detecting specific elements and assembling them into complex forms • Gestalt principles, such as figure and ground, proximity, closure, similarity, simplicity, and continuity, help explain how scenes are organized into discrete forms • Form perception often involves perceptual hypotheses, which are inferences about the distal stimuli that could be responsible for the proximal stimuli sensed Depth Perception • Binocular cues – clues about distance based on differing views of the two eyes • Retinal disparity – refers to the fact that the right and left eyes see slightly different views of objects • Monocular cues – clues about distance based on the image in either eye alone • Pictorial cues – monocular cues that can be given in a flat picture, such as linear perspective, texture gradients, relative size, height in plane, interposition, and light and shadow The Auditory System Sound Waves Vary in: • Amplitude which affect perceptions of loudness • Wavelength which affects
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