Myers EXPLORING PSYCHOLOGY Module 14 Introduction to Sensation and Perception: Vision James A. McCubbin, PhD Clemson University Worth Publishers

Sensation  Sensation  the process by which our sensory receptors and nervous system receive and represent stimulus energy  Perception  the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

Sensation  Our sensory and perceptual processes work together to help us sort out complex images

Sensation  Bottom-Up Processing  analysis that begins with the sense receptors and works up to the brain’s integration of sensory information  Top-Down Processing  information processing guided by higher-level mental processes  as when we construct perceptions drawing on our experience and expectations

Sensation: Basic Principles  Psychophysics  study of the relationship between physical characteristics of stimuli and our psychological experience of them  Light- brightness  Sound- volume  Pressure- weight  Taste- sweetness

Sensation: Thresholds  Absolute Threshold  minimum stimulation needed to detect a particular stimulus 50% of the time  Difference Threshold  minimum difference between two stimuli required for detection 50% of the time  just noticeable difference (JND)

Sensation: Thresholds  Subliminal  when stimuli are below one’s absolute threshold for conscious awareness LowAbsolute threshold Medium Intensity of stimulus Percentage of correct detections Subliminal stimuli

Sensation: Thresholds  Weber’s Law  to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)  light intensity- 8%  weight- 2%  tone frequency- 0.3%

Now you see it, now you don’t! Sensory Adaptation- diminished sensitivity as a consequence of constant stimulation

Vision  Transduction  conversion of one form of energy to another  in sensation, transforming of stimulus energies into neural impulses  Wavelength  the distance from the peak of one wave to the peak of the next

Vision  Hue  dimension of color determined by wavelength of light  Intensity  amount of energy in a wave determined by amplitude  brightness  loudness

The spectrum of electromagnetic energy

Vision: Physical Properties of Waves Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Great amplitude (bright colors, loud sounds) Small amplitude (dull colors, soft sounds)

Vision

 Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina  Retina- the light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of neurons that begin the processing of visual information

Retina’s Reaction to Light- Receptors  Rods  peripheral retina receptors  detect black, white and gray  for peripheral or twilight conditions  Cones  receptors near center of retina  fine detail and color vision  for daylight or well-lit conditions

Retina’s Reaction to Light  Optic nerve  nerve that carries neural impulses from the eye to the brain  Blind Spot  point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there

Vision: Receptors Receptors in the Human Eye ConesRods Number Location in retina Sensitivity in dim light Color sensitive?Yes Low Center 6 million No High Periphery 120 million

Pathways from the Eyes to the Visual Cortex

Visual Information Processing  Feature Detectors  nerve cells in the brain that respond to specific features  shape  angle  movement Stimulus Cell’s responses

Visual Information Processing  Parallel Processing  simultaneous processing of several aspects of a problem simultaneously

Visual Information Processing  Trichromatic (three color) Theory  Young and Helmholtz  three different retinal color receptors  red  green  blue

Visual Information Processing Opponent-Process Theory- opposing retinal processes enable color vision “ON”“OFF” red green green red blue yellow yellow blue black white white black

Visual Information Processing  Color Constancy  Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object

Color-Deficient Vision  People who suffer red-green dificiency have trouble perceiving the number within the design

Opponent Process: Afterimage Effect