Midterm Results ScoreGradeN 42-53A B C D F7 Top score = 50 Top score for curve = 47 (2 people)
Verbal Imagery vs Visual Imagery The mind operates upon internal representations of knowledge. How is visual information (imagery) represented in memory? Paivio’s Dual-Code Theory – memory is better if we encode information visually and verbally. Separate representations are maintained for verbal and visual information.
Behavioral Evidence for Dual Codes Santa compared linear and spatial arrays of: Three geometric objects Three names of geometric objects Subjects were asked whether the arrays contained the same objects or names. Subjects were faster when shapes were in the same spatial arrangement but faster when words were linear.
Evidence From Brain Imaging Subjects were asked to mentally rehearse: A word jingle Navigating their neighborhood Increased blood flow occurred in different areas of the brain, depending upon the task. The same brain areas were active as when actually speaking or seeing.
Brain Evidence for Dual Codes
Mental Rotation Shepard – two-dimensional and three- dimensional mental images are rotated in the same way as actual objects. The more an object is rotated, the longer it takes to respond in a same/different task. Georgopoulos et al. – measured neurons firing in monkey brains when moving a handle. Intermediate cells fire showing rotation.
Shepard & Metzler’s Results 2D3D
Image Scanning Brooks – subjects scanned imagined diagrams (like letter F) and noted outside corners, or sentences noting nouns. Respond by saying “yes” or “no” Tap left hand for “yes,” right hand for “no” Point to Y or N on a sheet Scanning a sheet for Y’s & N’s conflicted with scanning the mental image. Conflict is spatial not visual.
Mentally imagine the F and scan the outline beginning at the *. Point to Y if an outside corner is present or N if not.
Pointing Was Slowest
Comparing Visual Quantities Time to make a judgment decreases as the difference in size between objects increases. The smaller the difference the longer it takes to make a judgment. Which is larger: moose or roach, wolf or lion? The same pattern emerges when asked to judge actual differences, line lengths.
Which is bigger? The closer in size, two animals are, the longer it takes to decide which is bigger.
Two Types of Imagery Images involving visual properties (what) -- impaired with temporal damage. Images involving spatial properties (where) – impaired with parietal damage. Bilateral temporal lobe damage: Difficulty judging color, size, shape. No deficit in mental rotation, image or letter scanning, judgment of relative positions.
Are Images Like Perception? A series of experiments to compare perception and imagery: Imagining transformations of mental images vs perceived stimuli. Ponzo illusions occur with imagery. Difficulty with reversible figures – depends on instructions, harder. MRI plots show same brain activity.
Similar Brain Activity Fusiform face area Parahippocampal place area
Is Imagery Epiphenomenal? Does imagery play a functional role in thinking or is it a subjective side-effect? Kosslyn et al. showed that subjects could make judgments about arrays held in mind: Which has longer stripes? Visual regions (V17) became active during imagery.
Cognitive Maps Two kinds of maps: Route map – indicates places and turns, but not all landmarks. Survey map – shows all relevant portions of space, not just route. Adults produce survey maps, kids produce route maps. Survey maps more versatile.
Examples Disneyland to Cal Poly Pomona via Yahoo Maps &lon= &zoom=12&q1=disneyland%2 C%20anaheim&q2=3801%20W%20Tem ple%20Ave%2C%20Pomona%2C%20C A%2C%
Navigation Navigation is complicated by the need to tie together different kinds of mental representations. Egocentric representation – space “as we see it” Allocentric representation – not specific to a particular viewpoint Most maps are allocentric
Types of Representations Egocentric Allocentric
Thinking About Maps People rotate physical maps to fit their egocentric perspective. When the map itself cannot be rotated, extra processing time shows that people rotate an image of the map in their heads. Cognitive maps show no orientation effects. Allocentric representations are maintained by the hippocampus.
Map Distortions Which is farther east: San Diego or Reno? People make wrong guesses because they reason from the positions of the states, not cities. Relative positions of larger areas are compared, not details – hierarchical chunking.
Which is farther East: San Diego or Reno? Which is farther North: Seattle or Montreal? Which is farther West: the Atlantic or the Pacific entrance to the Panama Canal?
Translating Verbal Descriptions Subjects were asked to read passages, rotate themselves and make judgments: Fastest when making above-below judgments, slower with right-left. Verbal directions (survey or route) are as good as using actual maps.
Franklin & Tversky’s Study Some directions are faster to interpret verbally and orient ourselves in than others.
Overlap of Visual Perception and Visual Imagery