Perception We are at the beginning of a new section of the course. While the first section focused on the underlying basis of our behavior, the focus of this section will be on our thinking. We will start with the input to the process, sensing the world. This of course was also an issue in the last section of the course where we saw that behavior often began with a stimulus that had to be sensed (think of the knee jerk example, or a taxis). Big question: Why don’t we see the world as it is: the Missouri issue!

Perception The nativist-empiricist debate (does all information come in via the senses or is some innate)? Top-down and bottom-up perception and the issue of why we don't see the world as it is. The ear and audition. Volley and Place theories of hearing. Operating characteristics of the auditory system Psychophysics: measuring the response of sensory systems, including absolute and difference thresholds. The just noticeable difference (jnd) and Weber's and Fechner's law. Power functions (Stevens) and its neural counterpart.

Nativism-Empiricism Empiricists: All information is acquired via experience, thru the senses –The mind as a blank slate –British movement, John Locke Nativists: Some information is innate - Nothing in the mind but the mind itself -German movement, Immanuel Kant

The perceptual challenge Constructing a perception of the distal stimulus from the proximal stimulus Top-down and bottom-up perception –Bottom up: start with distal stimulus (sensory data) and build up representation –Top down: start with expectations & context to help sense/interpret incoming data stream

Automaticity of the process: The Stroop Effect

Perception The nativist-empiricist debate (does all information come in via the senses or is some innate)? Top-down and bottom-up perception and the issue of why we don't see the world as it is. The ear and audition. Volley and Place theories of hearing. Operating characteristics of the auditory system Psychophysics: measuring the response of sensory systems, including absolute and difference thresholds. The just noticeable difference (jnd) and Weber's and Fechner's law. Power functions (Stevens) and its neural counterpart.

Theories of Audition Volley Theory (aims at temporal orientation of auditory sense) Place Theory (Von Bekesy) Concept of lateral inhibition

Perception The nativist-empiricist debate (does all information come in via the senses or is some innate)? Top-down and bottom-up perception and the issue of why we don't see the world as it is. The ear and audition. Volley and Place theories of hearing. Operating characteristics of the auditory system Psychophysics: measuring the response of sensory systems, including absolute and difference thresholds. The just noticeable difference (jnd) and Weber's and Fechner's law. Power functions (Stevens) and its neural counterpart.

Pschophysics (Mind-World Relationship) Absolute threshold Difference threshold (jnd) = just noticeable difference Weber’s Law Weber-Fechner Law

Modified View of all this… Magnitude Estimation Steven’s Law: Power Function Cross Modality Match

Power Functions (vs. Weber) (r) a = (s) b Magnitude Estimation Steven’s Law: Power Function Cross Modality Match

Visual system characteristics Retina: 120 million rods & 6 mill. Cones Retinal distribution meaningful

System operating characteristics Color Sharpness or acuity: 1 sec. line (1 inch at 3.5 miles) Sensitivity (range (candle at 10 mi. to noon sun 10,000,000,000,000:1) Differential course of adaptation

Duplex Theory of Vision Two systems: –Rod based Sensitive Low acuity Monochromatic –Cone based High threshold High acuity Color

Adaptation Overall range of light : 1 Adaptation range of eye 10 5 : 1

We’re not from Missouri! Color Vision ( Perceptual constancies/neural interactions) Feature Detection--the analysis of visual input –Limulus –Cats –Humans Top-down perceptual processes and their interactions with bottom-up

Active processing Sentence Necker Cube Gestalt principles

Brief Story The large black dog was chasing the the pretty little groundhog who was very much afraid of him across the carpet.

Feature Detection: The Analysis of Visual Input Bottom-up perceptual processes (lateral inhibition) –Limulus (Hartline & Ratliff) –Frogs (Matarana, Lettvin, McCullough & Pitts) –Cats (Kuffler, Hubel & Weisal) –Humans Top-down perceptual processes and their interactions with bottom-up

Top-down processes: Some examples and a mechanism

Word Superiority Effect & its Mechanism

Conclusion Perception is an active process that tries to extract a more or less coherent iinterpretation of the world from the barrage of stimuli impacting us. It focuses on change (temporal or spatial). In order to quickly extract info from the deluge, it must distort the world to attempt to see it for what it is!!