Perception

1. Perception The process of organizing and interpreting information, enabling us to recognize meaningful objects and events. We see not how the world is but how it is useful to us

2. Selective Attention • The focusing of conscious awareness on a particular stimuli • You didn’t notice consciously feel your shirt until you read this  • Inattentional Blindness: failing to see visible objects when our attention is directed elsewhere • Change Blindness: failing to notice changes in the environment Click on the mouse to see an example of change blindness.

3. Cocktail-party phenomenon • The cocktail party effect describes the ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations • Form of selective attention

4. Top-Down Processing • We identify something b/c our brain tells us what the object is (prior knowledge) • We perceive by filling the gaps in what we sense. • I _ant ch_co_ateic_ cr_am. • Based on our experiences and schemas. • If you see many old men in glasses, you are more apt to process a picture of an old man (even when you may be in error).

5. Bottom-Up Processing • Also called feature analysis • We use the features on the object itself to build a perception • No prior knowledge • Takes longer than top-down but is more accurate Click to see an example of bottom –up processing.

6. Thresholds • Absolute Threshold: the minimum amount of stimulation needed to detect a light, sound, pressure, taste, odor… 50% of the time • Psychophysics: the study of relationships between physical characteristics of stimuli (like intensity) and our psychological experience of them (look for absolute thresholds) • Ex: mtn on dark night, see light miles away • Ex: hearing tests • Ex: mosquito ring tones • Ex: shopkeeper

7. Signal Detection Theory Ex: wartime • Theory that predicts when we detect weak signals amid background stimulation • Says absolute thresholds are not really absolute • So many factors affect what we can sense • time of day? did you eat breakfast? do they exercise? Did you get enough sleep? … • 4 possibilities: • Hit-signal present & sensed • Miss-signal present but not sensed • False Alarm-signal not present but sensed • Correct Rejection-signal absent & not sensed

8. (Just Noticeable Difference) Difference Threshold • The smallest amount of change needed to detect in a stimulus before we detect a change • Why would you need this? • Ex: hearing your friend’s voice over other voices in the hallway • Ex: My mom’s whistle • Ex: Musician detecting differences when tuning an instrument

9. Weber’s Law • The greater the magnitude of the stimulus, the larger the differences must be to be noticed • Ex: if you are listening to the tv at volume 40, the JND occurs when you decrease the volume by 4 • If you are listening to tv volume at 20, the JND occurs when you decrease the volume by 2

10. Perceptual Ideas

11. Figure Ground Relationship • We organize what we see into objects (the figures) that stand out from their surroundings (the background) • We always organize stimulus into a figure seen against the ground

16. Gestalt Psychology • Gestalt psychologists focused on how we GROUP objects together • We innately look at things in groups or as a WHOLE, not as isolated elements (we want to see the forest, not the trees) • Proximity (group objects that are close together as being part of same group- 3 sets of 2 lines, not 6) • Similarity (objects similar in appearance are perceived as being part of same group- vertical columns of similar shapes not horizontal of different) • Continuity (objects that form a continuous form are perceived as same group- 1 wavy, 1 straight line) • Connectedness (b/c they are uniform & linked we think of the 2 dots and line as one unit) • Closure (like top-down processing…we fill gaps in if we can recognize it) CLOSURE

17. Depth Cues • Depth Perception: ability to see 3D, allows us to judge distance • Our retinas pick up 2D but we see 3D • Eleanor Gibson and her Visual Cliff Experiment. • If you are old enough to crawl, you are old enough to see depth perception. • We see depth by using two cues that researchers have put in two categories: • Monocular Cues • Binocular Cues

18. Binocular Cues • Binocular Cue: depth cues that depend on the use of 2 eyes • Retinal Disparity: the difference between the images each eye perceives • Each eye sees different things • important for depth perception • Let’s see this in action!!!

19. Monocular Cues Monocular Cue: You really only need one eye to use these (used in art classes to show depth) Linear Perspective: parallel lines appear to converge w/ distance Interposition: if one object partially block our view of another we think it’s closer

20. More Monocular Depth Cues Relative Height: we perceive objects higher in our field of vision as farther away Relative Size: the smaller the object the farther away we think it is Light and Shadow: given 2 identical objects the dimmer one seems farther away

21. Perceived Motion Stroboscopic effect (flip book effect, cartoons) Phi phenomenon: movement illusion when 2 or more adjacent lights are blink on and off in quick succession Autokinetic Effect (if people stare at a white spotlight in a dark room, it appears to move)

22. Perceptual Constancy • Perceptual Constancy: perceiving objects as unchanging even when light and retinal images change • Shape Constancy • door • Size Constancy • Car carrying people • Color Constancy

23. Perceptual Constancy • Size Constancy • Lightness Constancy • Color Constancy • You saw all of these in the “Brain Games” video

24. Perceptual Set • What do these letters spell? FOLK • How about these? CROAK • And these? SOAK • What do we call the white of an egg? • NO!!! IT’S AN EGG WHITE!!! • Perceptual Set: a mental predisposition to perceive one thing and not another