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We know the most about the visual system so we’ll start there 1. The sense organ gathers and focuses light 2. Photoreceptors are receptor cells on the retina retina lens lens iris pupil retina The pupil and iris control the amount of the light The lens controls the sharpness of the light 3. The optic nerve connects eye to brain We can describe the ear and its parts in the same way that we describe the eye and its parts 1. The outer and middle ear 2. Hair cell 4. The visual cortex (in the occipital lobe) receives and interprets the nerve signal 3. The Auditory nerve 4. The Auditory cortex 1 DISTAL STIMULUS (Stimulus in the world) PROXIMAL STIMULUS (Stimulus “in your head”) (Brain activity) The proximal stimulus is experienced as a sensation Psychologists have approached this problem in two ways: (1) by looking at the most basic stimulus unit (2) by looking at the whole object/scene small black cat, smaller red ball, This distinction has led psychologists to either: (1) study the processing limits of individual stimuli (psychophysicists: bottom-up) OR (2) to study how entire scenes or objects are processed (Gestalt and ecological psychologists: top-down). Psychological Experience Level of brightness “Psychophysicists” ask questions like… 1. What is the minimum stimulus that will create a psychological experience (a sensation)? 2. How does psychological experience change when the stimulus changes? 3. What happens when the stimulus remains constant over time ? 2 2. How does psychological experience change when the stimulus changes? Brightness Estimate 1. What is the minimum stimulus that will create a psychological experience? 15 10 5 0 0 5 10 15 Physical Energy (Watts) One unit of physics ≠ One unit of psychology What is the threshold of a mental experience? The amount of change in stimulation required before you notice a change is called the Just Noticeable Difference 3. What happens when the stimulus present remains constant over time ? Weber’s Law: is related to Level of Stimulation Present Loudness estimate JND A major lesson of psychophysics: Psychological experience is measurable but there is a difference between the stimulus and our experience of it 10 5 0 0 5 10 15 Time (minutes) 3 Summary (1) Sensory systems consist of (a) a sense organ, (b) receptors, (c) nerve cells (neurons), and (d) a brain area. (2) Sensory systems turn a distal stimulus (outside the head) into a proximal stimulus (inside the head) to create our sensations (what we “feel”). (3) Study of sensations has focused on basic unit (bottom up) or whole scene (top down) processing. (4) Psychophysicists study basic stimuli to determine how our sensations map onto the amount of the stimulus present. (5) Study of psychophysics has shown that with a change in stimulus, sensations do not change in the same way. How do you perceive a 3-D world? How is the proximal stimulus interpreted? DISTAL STIMULUS (Stimulus in the world) PROXIMAL STIMULUS (Stimulus “in your head”) (Brain Activity) PERCEPTUAL EXPERIENCE (Interpretation of the proximal stimulus) What kind of cues are available from the image on the retina? CUE #1: Retinal image size The retina is a flat (and curved) surface 4 CUE #2: Interposition (Occlusion) CUE #3: Linear perspective Sheba Bert Vs. Vs. Sheba Bert 5 FIGURE-GROUND PROBLEM (3) Another way that psychologists have looked at perception is terms of the function that a particular object affords. In other words, objects are perceived in terms of “what they can be used for”. APPARENT MOVEMENT or PHI PHENOMENON Summary (1) While psychophysicists focused on measuring sensations, other perception psychologists focused on perceptions (our interpretation of the sensations). (2) One way psychologists have suggested we do this is by using clues in the scene to determine the distance or size of objects in the scene. However, clues can be ambiguous and illusions may result from errors in interpreting the clues. (3) Alternatively, Gestalt psychologists suggested we interpret scenes in terms of the patterns we detect in them (organizational processing). Illusions result from seeing more than one pattern in a scene. (4) Similarly, ecological psychologists suggest we process stimuli as a whole based on what they allow us to do (function). 6