Perception and Sensation

• Perception is the integration of stimulation from the senses and involves inferences and top-down processes.

• Top-down processes involve memory, expectations, mood, current context, and beliefs in interpreting sensory information.

• Examples of inference in perception include perceptual constancy, which allows us to perceive the world consistently despite variations in raw data received by the brain.

Perceptual Constancy

• Perceptual constancy refers to our perception of size, shape, color, and brightness remaining constant despite changes in distance or lighting conditions.

• Examples of perceptual constancy include perceiving the size of an object as constant regardless of its distance, perceiving the shape of a door opening, perceiving the color of a friend's face as the same whether it is day or night, and perceiving a white wall as bright even at night.

Brightness Contrast

• Our perception of brightness is not solely dependent on the absolute amount of light reflected from an object but also on the amount of light reflected from other objects in the vicinity.

• Brightness contrast is different from brightness constancy.

Top-Down Processes in Perception

• Top-down processes in perception involve filling in gaps, phonemic restoration, illusory contours, and degraded figures.

• Perceptual set refers to the readiness to interpret stimuli in a certain way based on expectations, experience, and psychological state.

Ambiguous Figures

• Ambiguous figures can be perceived in two different ways, based on the same raw material from the senses.

• Perceptual set can bias the interpretation of ambiguous figures.

• Examples of ambiguous figures include "THE CAT" example, where the context of other letters defines how the ambiguous stimulus is perceived, and the Necker Cube.

Perception and Reality

• The question of whether we objectively experience reality arises when we consider that our interpretation of the world is subjective.

• Examples of challenges to objective reality include Descartes' malevolent demon and virtual reality.

• Some aspects of objective reality may be beyond the range of sensation or perception, such as dog whistles or infrared rays.

Visual Perception and Depth Perception

• Visual perception involves the ability to locate objects and judge distance.

• Depth perception includes absolute distance and relative distance.

• Binocular depth cues, such as convergence and binocular disparity, provide information about depth perception.

• Monocular depth cues, such as motion parallax, relative size, linear perspective, texture gradient, aerial perspective, and occlusion, also contribute to depth perception.

Visual Illusions

• Visual illusions occur when top-down processes fool us.

• Examples of visual illusions include the Muller-Lyer illusion, Ponzo illusion, and Ames room illusion.

Auditory Perception and Locating Objects

• The ability to locate the source of sound is innate, and newborns will turn their heads to face sound.

• Auditory perception of locating objects is based on differences in sound intensity at the two ears, overall sound intensity, and differences in the time it takes for sound to reach each ear.

Motion Perception

• When examining a stable object, our perceptual system compensates for voluntary eye movements, resulting in a stable image.

• If we move our eyes with something other than eye muscles, the perceptual system can't compensate, and we perceive the object as moving.

• Motion perception involves distinguishing between the object moving and the observer moving, using background changes relative to the object and auditory cues.

Illusions of Motion

• Apparent motion occurs when the perceptual system fills in the gaps between successive, motionless images.

• Examples of apparent motion include motion pictures and the phi-phenomenon, which is apparent motion produced by a succession of flashing lights.

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• Phi Phenomenon and Illusions of Motion

  • Apparent motion

    • Induced motion: objects near a stationary one appear to be moving

      • Example: clouds in front of the moon on a windy night

      • Example: objects under the water in a stream

    • Motion after-effect: after moving forward and then stopping, scenery outside seems to move backward slightly

• Perception of form and recognition of letters

  • Controversy between Gestalt (whole first, then parts) and feature analysis (parts first, then whole)

  • Feature analysis: bottom-up processes

    • Different feature detectors are activated when a stimulus is presented

    • Activated feature detector cells activate different stored representations of letters in memory

    • The most activated memory representation wins

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• Feature Analysis

  • Perceptual system recognizes objects based on features

  • Gestalt

    • "The whole is greater than the sum of the parts"

    • Understanding perception by examining the system at a higher level

  • "Filling in the gaps"

    • Perceptual system completes missing pieces to make a holistic interpretation

  • Perceptually Ambiguous Figures

    • Gestalt or organization can "flip" to obtain a new interpretation

    • Can't see both Gestalts at once, they "flip back and forth"

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• Formation of Gestalts

  • Organizing Principles

    • Figure/ground distinction: distinction between what stands out (figure) and what is background (ground)

    • Grouping Principles

      • Proximity

      • Good continuation

      • Closure

  • Ambiguous Figure/Ground

    • Example: M.C. Escher's Mosaic II

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• Gestalt Principles Applied to Sound Perception

  • Figure-ground distinction: speaker as figure, audience sound as ground

  • Grouping Principles

    • Proximity of notes in a song allows hearing successive notes as belonging to a melody

    • Good continuation allows picking out the melody in the presence of background harmonies

    • Closure allows filling in gaps of a radio announcer competing with static

• Perceptual ambiguity in audition is similar to visual perception: only one organization of sound can occur at once

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• Gestalt Principles and Problem Solving

  • AHA! type problems can be organized into a particular Gestalt, but suddenly "flip" to a new interpretation to solve the problem

  • People may be fixated on one organization of the problem, solving it involves a sudden flip to a new Gestalt

  • Insight Problems

    • Example: A father and his son are in a car accident. The father dies at the scene and the son is rushed to the hospital. At the hospital, the surgeon looks at the boy and says "I can't operate on this boy; he is my son." How can this be?

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• Nature/Nurture and Perceptual Organization

  • Evidence for Nature (inborn)

    • Infants at 6 months respond to depth cues, shown by the visual cliff experiment

    • Newborns show preference for shapes resembling human faces

  • Evidence for Nurture (learning)

    • Feature detector cells can be trained to be sensitive to particular orientations

    • Perceptual adaptation and differentiation

      • Adaptation: example of Stratton

      • Differentiation: experience refines perception, trained musicians can hear subtleties in harmony that others would miss

      • Reading ability relies on perceiving subtle