PSY 2012 General Psychology Chapter 5: Sensation and Perception Samuel R. Mathews, Ph.D. Associate Professor The Department of Psychology The University of West Florida

Environmental Stimuli Sensory Organs Brain Stimuli must exceed the threshold necessary to trigger the sense receptors in the sense organs Sense organs change the physical stimuli into electrochemical energy that travels across the neural pathways in a process termed transduction The brain converts the neural impulses to the experiences we report of sight, sound, touch, smell, taste, etc. Sensation

Key Concepts in Sensation Transduction: the process of converting physical energy (e.g., light, sound waves, pressure) to electrochemical energy in the cells of the sense organs Sensory Adaptation: the process of our sense organs becoming habituated to levels of stimulation in our environment (e.g. losing sensitivity to the experience)

Key Concepts in Sensation Thresholds: Sensitivity of the sense organ –Absolute threshold: lowest level of physical energy a sense organ can detect –Difference threshold: the minimal difference between two levels of a given stimulus for which a difference can be detected.

Did you see that? Or Signal Detection Theory Sense organs’ abilities to detect the presence or change in a stimulus is based on: –Signal strength and quality –Background noise –Expectations or mental set –Prior experience with the stimulus –Fitness/health of the organ itself

The Human Eye l

Light Energy Eyes Parietal and Occipital Lobes Light energy varies in wave length (within the electromechanical spectrum) which produces color and intensity or amplitude which produces brightness Transduction occurs in the retina of the eye in specialized cells (rod & cone cells) that detect color and intensity The optic nerve via the bipolar cells and ganglion cells transmits the signals from the retina to the brain. These signals feed primarily to the parietal lobe and visual cortex of the occipital lobe. Visual Sensation

Color Sensation Cone cells, concentrated in the fovea of the eye are sensitive to color but require relatively high levels of light to “fire” Initial process of color sensation is the stimulation of 3 types of cone cells (each type senses either red, blue, or green) in the retina of the eye—the trichromatic process The second phase of color sensation is in the bipolar cells and operates within the opponent-process theory –Cone cells transmit nerve signal to the bipolar cells –Opposing colors cancel each other out (red and green are opponent colors and yellow and blue are opponent colors) –The results of this process are transmitted to the brain via the optic nerve.

Opponent Process Theory + +

Seeing in the dark or The Perception of Brightness Rod cells –Sensitive to lower levels of light; –Located around the periphery of the fovea; –Responsible for so-called night vision Note: Night vision can be enhanced by looking slightly away from the object in darker situations. Rod cells are more densely concentrated outside the fovea of the eye.

Did you hear that? or Auditory Sensation

Sound Waves Ears Temporal Lobe Sound waves vary in frequency (Hz or CPS) that relates to pitch and amplitude (peak-to-peak within a cycle) that relates to volume Transduction occurs in the ear as the sound waves impact the tympanic membrane which sets up vibrations impacting bones (hammer, anvil, & stirrup) which pass vibrations to the cochlea stimulating the basilar membrane which converts the energy to neural signals The auditory nerve transmits the signals from the inner ear to the brain. These signals feed primarily to the auditory cortex of the temporal lobe Auditory Sensation

Qualities of Sensation of Sound Pitch: –Based on the frequency of the sound waves; –20Hz to 20,000Hz is the normal range for humans with healthy hearing sense –Location on basilar membrane that receives the greatest stimulation represents one system of picking up pitch above 1000Hz (place theory); –Basilar membrane neurons rate of firing based on frequency is related to sounds below 5000Hz (frequency theory). –Between 1000Hz and 5000Hz is the range of typical human speech—hence redundancy.

Qualities of Sensation of Sound Loudness –Based on amplitude of the sound waves Frequency=number of cycles/second AMPLITUDEAMPLITUDE 1 Cycle

Qualities of Sensation of Sound Timbre: –Characteristic sound of a particular event (e.g. dog barking, door slamming, heavy metal guitar rip) Attack and decay: the onset and duration of a sound coupled with the intensity and rise or fall of the sound volume Vibrato: periodic change in pitch of the tone Harmonic content: the complexity of the tone combinations

Other Major Senses Motion and position in space: –Vestibular sensation based on cilia (tiny hairs) in the inner ear; As our head moves, fluid in the semicircular canals stimulate the cilia and stimulate nerve cells that give us the sensation of motion Conflicts between vestibular sensation and other motion cues coming from vision can bring about motion sickness Inner ear infections can lead to similar experiences –Kinesthetic sensation based on feedback from muscles Allow us to position our extremities in space With vestibular sense we are aware of our spatial position –Vestibular and Kinesthetic sensations are processed in the parietal lobe and lead to awareness of our spatial position

Making Sense of our Senses: Perception Once the sensation is detected (signal detection theory) the mind begins to “make sense” of the sensory experience. This involves: –Interpreting (naming, recognizing) –Organizing (creating structures based on existing mental structures or creating new structures) –Perceptual experiences typically involve higher cognitive functions and rely on top-down and bottom-up processes

Perception Bottom-up Processes: –These processes are “driven” by the sensory experiences created from the stimulus from the environment; –Distinctive features of the stimulus control our representation of that stimulus (e.g. color, motion, texture) Top-down Processes: –Processes driven by the individual’s biases, expectations, motives, and existing knowledge –Features of the stimulus can be interpreted in a number of ways depending on the state of the organism –The organism “constructs” unique precepts from the sensory experiences –Frequently the perceptual experience is at odds with the “reality” of the stimulus

Perception Perceptual constancy: –Stability of members of a category of objects or events; –Based on shared attributes –Identification of objects/events is constant even with highly different sensory experiences –Top-down driven based on experience and expectations about the objects or experiences Shape constancy Color constancy Etc.,

Perception Bridging the top-down and bottom-up process: –Sense organs are “wired” to detect particular features of the environmental stimuli –Once detected, the sensory experience and the expectations, motives, and mental set of the organism bring to the experience a set of plausible interpretations. Therefore, perception is a hybrid of top-down and bottom-up processes.

Perceptual Theories Gestalt Theory: –Human beings evidence a tendency to aggregate elements of a stimulus array into an organized pattern or array; –This pattern or array is the basis from which we interpret sensory information into perceptions. –Such interpretations are always based on incomplete sensory information and reflect individual experience

Figure Ground Perceptual Organization

Closure Perceptual Organization

X O X O X O X Perceptual Grouping Law of Similarity

X O X O X O X Perceptual Grouping Law of Proximity

Depth Perception Binocular Cues (both eyes) –Binocular Convergence: degree to which the two eyes must converge to focus on the object –Retinal Disparity: difference in perspective of the two images on the retina

Depth Perception Monocular Cues (single eye depth perception) –Relative Size: for objects known to be similar in size, the one seen to be larger is perceived to be closer –Interposition: if one object hides part of another, the one hiding the other is perceived to be closer –Relative Motion: objects at different depths from the eye appear to move at different rates when the individual is in motion (closer objects appear to “move” more quickly)

Perceptual Set: Seeing what we expect Expectations can influence what we are “ready” to perceive Contextual “set-ups” can prepare us to one interpretation vs. another Perception is NOT reality; it is OUR reality