Perception Our conscious attention is selective.
Getting Started • Reading Handout • True false • PsychSim 5 • Visual Illusions; complete for next class
Which Line Is Longer? From Perplexing Puzzles and Tantalizing Teasers, (p.75), by Martin Gardner, 1988, New York Dover.
Perception • The process in which people take raw sensation from the environment and interpret them • Uses knowledge, experience and understanding • Sensations thus become meaningful experiences with perception
Three Approaches to Perception • Computational • Focuses on how the nervous system manipulates any incoming signals • Constructivist • Emphasizes the inferences people make about the environment • Ecological • Emphasizes the information provided by the environment
Absolute Thresholds • Subliminal Stimuli • Stimuli too weak to be noticed • Supraliminal Stimuli • Stimuli that are strong enough to be consistently perceived • The airplanes that fly overhead in this classroom!
Why Does the “Absolute” Threshold Vary? • Sensitivity: • Intensity of the signal. • Capacity of sensory systems. • Amount of background stimulation, or “noise.” • Response criterion reflects one’s willingness to respond to a stimulus. • Influenced by motivation and expectancies.
Signal Detection Theory • Signal-detection Theory • Mathematical model used to determine whether or not a near-threshold has occurred • Theorists seek to understand why people respond differently to stimulus • Newborn parents will miss a loud noise, but here a baby’s whimper • In heightened security times you have more false alarms • In peacetime, a stronger signal is required before sensing danger
Signal Detection Theory Trade off: high criterion minimizes false alarms, but also increases misses
Perceptual Illusion & Organization • Our mind structures information in several ways: • Form Perception • Depth Perception • Motion Perception • Perceptual Constancy
Summary: Form Perception • Figure-Ground Organization • Reversible images • You can’t see both figure and ground at the same time • Grouping • Gestalt Principles • Proximity • Continuity • Similarity • Connectedness • Closure
Depth Perception • How is it that we perceive a 3-dimensional world when our eyes only project a 2-dimensional image on our retinas??! • Our brain uses different cues to perceive depth • Binocular disparity • Since we use both our eyes to focus on an image, the angles used by each eye to put the image on the fovea of our retina is used by the brain to perceive distance • Retinal disparity: a cure for perceiving depth; the greater the disparity the closure the object • Monocular disparity • Our brain also uses information from the stimulus that does not involve our use of both eyes (see next slide)
Stimulus Cues for Depth Perception • Monocular cues • Interposition • Relative Size • Relative height • Textural Gradient • Linear Perspective • Relative Clarity • Light and Shadow • Motion
Perception of Motion • Many cues come from optical flow. • Looming • When an image looms, you tend to interpret it as an approaching stimulus • Questions of Interest • How do we know whether flow of images across retina is due to movement of objects or own movements? • How do we compensate for the time-lag in the perception of movement?
Perception of Motion • Sometimes we perceive motion when there is none. • 3D movies and feelings of nausea • Stroboscopic motion: Illusion of movement when images are flashed in rapid succession • Flashing neon lights can appear to make the sign move
Perceptual Constancy • Perceiving objects as unchanging; having constant: • Size • The tendency to view an object as constant in size despite changes in the size of its image on the retina (as we move) • Shape • The tendency to see an object as retaining its form despite changes in orientation • Brightness
Perceptual Processing • Bottom-Up Processing • Analysis that begins with the sense receptors and works up to the brain’s integration of sensory information • 4 legs, round surface; must be a table • Top-Down Processing • Information processing guided by higher-level mental processes • We construct perceptions based on our experience and expectations • i.e. the jumbled sentence from lesson one
Top-Down Processing • Aided by higher level cognitive processes and expectation we transform information into meaningful experiences • Our experiences create schemas. • Schemas can bias our perceptions by creating a perceptual set (we perceive one thing not another). • Predisposition can also be shaped by the immediate context of the stimulus. • Motivation can affect perception. • Can even influence elements of the brain’s bottom-up processing (sensory receptors to brain).
Attention • We use attention to: • Direct our sensory and perceptual systems toward certain stimuli. • Select specific information for further processing. • Allocate the mental energy required to do that processing. • Regulate the flow of resources necessary for performing a task or coordinating several tasks at once.
Characteristics of Attention • Improves Mental Processing • Usually we need to concentrate to do our best • Takes Effort • Prolonged attention is tiring • Is Limited • Focusing on this lecture and making notes leaves less attention for hallway noises
Directing Attention • Voluntary, or goal-directed attention control reflects top-down processing • You purposely focus your attention in order to perform a task (writing) • Involuntary attention control reflects bottom-up processing • Attention redirected because of a loud noise
Divided Attention • Sometimes difficult to stop dividing attention (multitask) • Drive car, listen to music, shift gears, watch road signs • Attention is a limited resource. • Easier to do two things at once if one task is automatic.
Applications of Research on Perception; the Human Factor • Aviation Psychology • Landing the plane • Human-Computer Interaction • Trash can for the delete button • Traffic Safety • Driving performance and cell phones • Architecture and Interior Design • Window sizes to change the feel of the space
Is there ESP? • ESP is the controversial claim that perception can occur apart from sensory input • Telepathy • mind-to-mind communication • Clairvoyance • Perceiving remote events • Precognition • Perceiving future events (think Minority Report) • Parapsychologist • Those who study paranormal
Research on ESP • After thousands of experiments, a reproducible ESP phenomenon has never been discovered • Remember scientific study blends curious skepticism with open-minded humility • We do assume some tings to be true • God’s existence or non-existence • Someone else’s love • The finality of death or reality of life after it
Review • Jeopardy: final two columns • Some Questions • Top-down processing and the influences of expectancy, motivation and schemas. • Success of dual-attention tasks and why. • Describe how you would use at least five monocular cues to give a scenery painting a sense of depth.