Chapter 4 Sensation and Perception

Objectives 4.1 The Interaction of Sensation and Perception Distinguish between sensations and perceptions. Determine how they work together when processing an external stimulus. 4.2 Sensory Principles Apply the principles of transduction, thresholds, and adaptation across the senses.

Objectives 4.3 The Five Major Senses Identify the five main external senses. Describe how each sensory organ achieves transduction. Follow the path of signals within the brain.

Objectives 4.4 Perception Organizes Sensations Describe the Gestalt organizational principles. 4.5 Experience and Perception Give examples of how perception may be altered by experience. 4.6 The Role of Attention Describe how attention enhances and limits perception.

The Interaction of Sensation and Perception Sensation: The process of registering the stimulation of sensory receptors by an external physical stimulus Perception: The process of organizing sensory information to form a meaningful interpretation

Top-Down and Bottom-Up Processing Bottom-up processing: The stimulus-driven process of sensation that registers external physical energy and translates it into neural encoding Top-down processing: Perception through the use of information in memory to organize incoming sensations

Transduction of Physical Energy into Neural Stimulation Transduction: The process in which physical energy in the world is translated into an electrochemical signal that represents sensation in the brain Sensory receptors: Specialized cells in each sense organ that react to only particular kinds of external physical stimulation

Detection Thresholds Reflect Sensitivity Absolute threshold: The lowest amount of physical energy that can be detected reliably 50% of the time using a given sense organ Difference threshold: The smallest difference in sensation that is reliably detectable –Just noticeable difference (jnd): The smallest amount of change between two stimuli that a person can detect at least half of the time

Weber’s Law As the stimulus becomes stronger or larger, so does the just noticeable difference between it and other similar stimuli.

Subliminal Perception Sensation registered “below threshold,” without conscious awareness of its occurrence

Sensory Adaptation A change in responsiveness to the same stimulation in a sensory organ over time Figure 04.07: In a visual scene, movement may be the only visual cue that reveals the presence of danger; in this case, an alligator in a plant-covered swamp. © Kevin Winkler Photography/ShutterStock, Inc.

The Five Major Senses

The Sense of Vision

Photoreceptors Figure 04.10: A depiction of the eye, where the layers of cells in the retina are enlarged.

Optic Nerve and Neural Pathways Figure 04.12: Neural stimulation takes place in the retina, From there, signals travel to the optic chiasm, the thalamus "relay center," and finally to the occipital lobes.

Perceiving Color Trichromatic theory: Color vision relies on sensory receptors in the retina that process only red, blue, and green. Opponent process theory: Opposing, or complementary, colors are produced by differences in firing rates by complex cells within the retina. –Afterimage: The appearance of an illusion of color on a white surface after viewing its complementary color for a prolonged period

The Sense of Hearing Frequency: The wavelength of sound or light waves (the time distance between peaks) Timbre: The complexity or purity of sound provided by the combinations of sound waves

The Experience of Hearing Place theory: The notion that the pitch of a sound is determined by the location of the stimulation on the basilar membrane inside the ear Frequency theory: The notion that the firing rate of neurons is determined directly by the frequency (length of time between sound waves) of the sound Decibel (dB): The unit for measuring the loudness of sound

The Sense of Smell Figure 04.17: Unlike other senses, much of the neural processing of smell takes place in the sense organ itself, rather than the cortex.

The Sense of Taste Figure 04.18: Taste buds are the chemical receptors located in and around papillae in the tongue and mouth.

The Sense of Touch Figure 04.21: This map of the body shows that some areas have greater sensitivity (require less pressure to recognize touch, shown by shorter bars) than others. Source: Data from Weber, E. H. (1978.) E. H. Weber: The sense of touch. [translated from De pulsu, resorptione, auditu et tactu: Anatationes anatomicae et physiologicae by E. H. Weber, 1834]. New York: Academic Press.

Pain (slide 1 of 2) Figure 04.22: We can respond to pain messages quickly based on "interneurons" in the spinal cord that link incoming sensory and motor neurons.

Pain (slide 2 of 2) Gate-control theory: The notion that interneurons in the spinal cord act as a gate to block some sensory signals from going to the brain Placebo effect: Feeling benefit or improvement from a treatment known to have no effect

Perception Organizes Sensations Figure 04.27: Recognition of the form of an object like a cup may require piecing together constituent parts, represented as “geons.”

Gestalt Organizing Principles Figure and ground Perpetual grouping

Laws of Perceptual Grouping Similarity Proximity Continuity Closure Figure 04.28: Organizing principles make it so that Panel A is seen as rows of dots, while Panel B is seen as columns of dots. This is due to the similarity in color.

Visual Illusions Reversible figure Impossible figure Figure 04.30: Two opposing images. One shows a series of columns, while the other shows two figures facing one another in silhouette. Figure 04.31: In some visual illusions, the laws of perceptual organization help to construct an image that is impossible in the physical world. © Juriah Mosin/ShutterStock, Inc. © artsmela/ShutterStock, Inc.

Depth Perception Binocular cues –Retinal disparity –Convergence Monocular cues –Accommodation.

Perception of Motion Motion parallax: The interpretation that objects close to you are moving past you faster than objects farther away Kinetic depth effect: The movement of a three-dimensional object reveals its shape Phi phenomenon: A series of static images viewed in sequence are interpreted as a moving image

Perceptual Constancy (slide 1 of 2) Shape constancy Size constancy Brightness constancy Color constancy

Perceptual Constancy (slide 2 of 2) Ames room illusion: An illusion created by adding physical distortions to make a room appear to have a normal rectangular shape so that its contents appear to violate size constancy © Andrew Holt/Alamy Images

Experience and Perception Development Learning Culture

The Role of Attention Inattentional blindness: Failing to process an object clearly present in a scene Selective attention: Intentionally attending to one specific task Change blindness: A change occurs between two viewings of a scene, but it is not noticed

Divided Attention The process of attending to two or more tasks to perform them at the same time