Sensation and Perception

Sensation: the conversion of energy from the environment into a pattern of response by the nervous system. Perception: the interpretation of sensory information.

I. Sensing the World Around Us A. Stimuli: energies in the environment that affect what we do. B. Receptors: the specialized cells in our bodies that convert environmental energies into signals for the nervous system. C. Photoreceptors… 1) Cones: are utilized in color vision, daytime vision, and detail vision and are most plentiful around the center of the retina. 2) Rods: are adapted for vision in dim light and are most plentiful in the periphery of the retina. D. Fovea: the center of the human retina, and the location of the highest proportion of cones.

II. The Detection of Light A. Light: the stimuli that the visual system is designed to detect. B. Visible Light: a small portion of the electromagnetic spectrum, which is the continuum of all the frequencies of radiated energy.

III. The Structure of the Eye

IV. Common Disorders of Vision A. Myopia (nearsightedness): the person can focus well on nearby objects, but not distant ones. B. Hyperopia (farsightedness): the person can focus well on distant objects, but not on nearby ones. C. Glaucoma: increased pressure within the eyeball, causing damage to the optic nerve and loss of peripheral vision. D. Cataract: the lens of the eye becomes cloudy.

V. Dark Adaptation: the gradual improvement in the ability to see in dim light. Cones Rods

VI. Color Vision A. The Trichromatic Theory: our receptors respond to three primary colors. 1) Short wavelengths are seen as blue. 2) Medium wavelengths are seen as green. 3) Long wavelengths are seen as red. B. The Opponent-Process Theory: we perceive color not in terms of separate categories, but rather in a system of paired opposites. 1) Red vs. Green 2) Yellow vs. Blue 3) White vs. Black

C. The Retinex Theory… 1) Color Constancy: the tendency of an object to appear nearly the same color even though we see it in a variety of lighting conditions. D. Colorblindness 1) About 4% of all people are partly colorblind (8% of men, “1 out of 12”, and 1% of women). 2) Red-green colorblindness is the most common type. 3) Yellow-blue colorblindness is very rare. 4) Complete colorblindness is extremely rare.

VII. Perceiving the World Around Us A. The Perception of Minimal Stimuli B. Subliminal Perception: is the idea that a stimulus can influence behavior even when it is so weak or brief that we do not perceive it consciously. 1) Subliminal: below the sensory threshold. 2) Supraliminal: subtle, or faint, but still processed consciously. C. What subliminal perception CANNOT do… 1) Subliminal stimuli in advertisements… 2) Messages in music… 3) Subliminal audiotapes… D. What subliminal perception CAN do… 1) Priming…

VIII. Recognition of Patterns and Contrast Effects A. Face Recognition B. Size Contrast C. Brightness Contrast: how the apparent brightness of an object that you are looking at can be increased or decreased by the objects around it.

IX. The Feature-Detector Approach A. Feature Detectors: specialized neurons that respond to the presence of certain simple features, such as angles and lines. 1) The Waterfall Illusion 2) BUT, feature detectors can’t explain…

X. Gestalt Psychology: focuses on the human ability to perceive overall patterns. A. Visual Perception: is an active creation, not merely the adding up of lines and movement. 1) Figure and Ground: what’s the object of focus and what’s the background. 2) Reversible Figure: a stimulus that can be perceived in more than one way.

B. Gestalt Principles… 1) The principle of proximity: states that we perceive objects close together as belonging to a group. 2) The principle of similarity: states that we perceive objects that resemble each other as forming a group. 3) The principle of good continuation: states that we perceive lines as continuous even when they are interrupted. 4) The principle of closure: states that we fill in gaps in lines, or close familiar figures. 5) The principle of common fate: states that we group together objects that appear to be moving in the same direction.

XI. Perception of Movement and Depth A. Visual Constancy: our tendency to perceive objects as keeping their size, shape and color even though the image that strikes our retina changes from moment to moment. B. Distal Stimulus: the actual physical object in the world. C. Proximal Stimulus: the optical image on the retina of the physical object in the world. D. Shape and Size Constancy…

E. Vestibular System: works to keep the visual system informed of the movements of your head. F. Induced Movement: a visual illusion in which we incorrectly perceive the object as moving. G. Stroboscopic Movement: an illusion of movement created by a rapid succession of stationary images. H. Phi Effect: in which your brain creates motion from rows of adjacent lights blinking on and off sequentially.

I. Monocular Cues: needing only one eye. 1) Object Size: the same sized object produces a larger image on the retina when it is closer than when it is further away. 2) Detail: objects that are closer can be seen in greater detail than when they are farther away. 3) Interposition: nearby objects will obstruct objects that are farther away. 4) Texture Gradient: clusters of objects will seem more densely packed the farther away the clusters are. 5) Shadows: give clues to distance depending on size and position. 6) Motion Parallax: close objects will pass by faster than distant objects.

XII. Optical Illusions: misinterpretations of visual stimuli. J. Binocular Cues: depending on both eyes. 1) Retinal Disparity: is the difference in apparent position of an object seen by each retina. 2) Convergence: the degree to which our eyes must turn in to allow us to focus on a very close object. XII. Optical Illusions: misinterpretations of visual stimuli. A. The Moon Illusion