Sensation & Perception Chapter 5 This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network; preparation of any derivative work, including the extraction, in whole or part, of any images; any rental, lease, or lending of the program. ISBN:

Sensation and Perception Perception – interpretation, organization of internal or external events (involves awareness and activity) Sensation – immediate, basic experience generated by a stimulus

Sensation & Perception Processes

Transduction – Transformation of one form of energy into another Receptors – Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse Transduction

Thresholds Absolute threshold – Amount of stimulation necessary for a stimulus to be detected Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND) Weber’s law – Size of a JND proportional to intensity of stimulus

Signal Detection Theory Signal detection theory – Perceptual judgment as combination of sensation and decision-making processes Stimulus event Neural activity Comparison with personal standard Action (or no action)

Signal-Detection Theory A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process. Stimulus is Present Stimulus is Absent Response: “Present ” HitFalse Alarm Response: “Absent” MissCorrect Rejection

The senses all operate in much the same way, but each extracts different information and sends it to its own specialized processing region in the brain How Are the Senses Alike? And How Are They Different?

Sensory Adaptation Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while

An Eye on the World Cornea –Protects eye and bends light toward lens. Lens –Focuses on objects by changing shape. Iris –Controls amount of light that gets into eye. Pupil

The Structures of the Retina

An Eye on the World Retina –Neural tissue lining the back of the eyeball’s interior Two Photoreceptors: Rods: respond to dim light/movement (125 million) Cones: involved in color vision/detail (7 million)

Why the Visual System is not a Camera Much visual processing is done in the brain. –Some cortical cells respond to lines orientations (e.g. horizontal). –Other cells in the cortex respond to other shapes (e.g., bulls-eyes, spirals, faces). Feature-detectors

Hubel & Wiesel’s Experiment

Constructing the Visual World Form perception. Gestault Principles –“whole is more than the sum of the parts”

Form Perception Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns. Figure – Part of a pattern that commands attention Ground – Part of a pattern that does not command attention; the background

Examples “Gestault”

More “Gestault” Proximity –Seeing 3 pair of lines in A. Similarity –Seeing columns of orange and red dots in B. Continuity –Seeing lines that connect 1 to 2 and 3 to 4 in C. Closure –Seeing a horse in D.

Law of Prägnanz

Depth and Distance Perception How can you tell what is closer?

Depth and Distance Perception Binocular Cues: –Convergence –Retinal Disparity Monocular Cues: –Relative size, overlap, texture gradient, linear perspective, atmospheric perspective, shadow/shading, motion parralax

Visual Constancies The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce. –Shape constancy –Size constancy –Color constancy

Shape Constancy Even though these images cast shadows of different shapes, we still see the quarter as round

Bottom-Up and Top-Down Processing Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors

Context Effects The same physical stimulus can be interpreted differently We use other cues in the situation to resolve ambiguities Is this the letter B or the number 13?

Visual Illusions Illusions are valuable in understanding perception because they are systematic errors. In the Muller-Lyer illusion (above) Visual Illusions

The Ponzo Illusion Linear perspective provides context Side lines seem to converge Top line seems farther away –But the retinal images of the red lines are equal!

How Sound Waves Become Auditory Sensations Cochlea – Where sound waves are transduced

Taste Buds Photograph of tongue surface (top), magnified 75 times. 10,000 taste buds line the tongue and mouth. Children have more taste buds than adults.

Four Tastes Four basic tastes –Salty, sour, bitter and sweet. Different people have different tastes based on: –Genetics –Culture –Learning –Food attractiveness

Smell: The Sense of Scents Airborne chemical molecules enter the nose and circulate through the nasal cavity.. Receptors on the roof of the nasal cavity detect these molecules.

The Skin Senses Touch Temperature Pain

Perceptual Powers: Origins and Influences James J. Gibson : Direct Perception –Invariants and affordances Inborn abilities and perceptual lessons

Psychological and Cultural Influences on Perception “needs”, beliefs and emotions can influence perceptions of sensory information. Expectations based on our previous experiences influence how we perceive the world. –Perceptual Set Readiness to detect a particular stimulus in a given context We all are influenced by our culture/experience.

Perceptual Set What you see in the center figures depends on the order in which you look at the figures: –If you scan from the left, see an man’s face –If you scan from the right, see a woman’s figure

Extrasensory Perception Extrasensory Perception (ESP): –The ability to perceive something without ordinary sensory information –This has not been scientifically demonstrated (issues with reliability/validity) Three types of ESP: –Telepathy – Mind-to-mind communication –Clairvoyance – Perception of remote events –Precognition – Ability to see future events