1 / 18

Cognitive Processes PSY 334

Cognitive Processes PSY 334. Chapter 2 – Perception June 30, 2003. Visual Perception. Distal stimulus -- tree Proximal stimulus – image of tree on retina Percept – interpretation of proximal stimulus as a tree Size and color constancy. Information Coding.

vegaw
Download Presentation

Cognitive Processes PSY 334

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Cognitive ProcessesPSY 334 Chapter 2 – Perception June 30, 2003

  2. Visual Perception • Distal stimulus -- tree • Proximal stimulus – image of tree on retina • Percept – interpretation of proximal stimulus as a tree • Size and color constancy

  3. Information Coding • On-off cells in LGN feed into edge and bar detectors in the visual cortex. • Edge detectors – respond positively to light on one side of a line, negatively on the other side of the line. • Bar detectors – responds maximally to a bar of light covering its center.

  4. Marr • Depth cues (texture gradient, stereopsis) – where are edges in space? • How are visual cues combined to form an image with depth? • 2-1/2 D sketch – identifies where visual features are in relation to observer. • 3-D model – refers to the representation of the objects in a scene.

  5. Pattern Recognition • Classification and recognition occurs through processes of pattern recognition. • Bottom-up processes – feature detection • Top-down processes -- conceptually driven processing

  6. Object Recognition • Two stages: • Early phase – shapes and objects are extracted from background. • Later phase – shapes and objects are categorized, recognized, named.

  7. Disruptions of Perception • Visual agnosias – impairment of ability to recognize objects. • Demonstrate that shape extraction and shape recognition are separate processes. • Apperceptive agnosia (lateral) – problems with early processing (shape extraction). • Associative agnosia (bilateral) – problems with later processing (recognition). • Prosopagnosia – visual agnosia for faces.

  8. Gestalt Priniciples • Wertheimer, Koffka, Kohler. • Form perception – segregation of a display into objects and background. • Principles of perceptual organization allow us to see “wholes” (gestalts) formed of parts. • We do not recognize objects by identifying individual features.

  9. Five Principles • Proximity • Similarity • Good continuation • Closure • Common fate • Elements that move together group together.

  10. Examples • Gestalt principles of organization • Reversible figures

  11. Law of Pragnanz • Of all the possible interpretations, we will select the one that yields the simplest or most stable form. • Simple, symmetrical forms are seen more easily. • In compound letters, the larger figure dominates the smaller ones.

  12. Visual Illusions • Depend on experience. • Influenced by culture. • Illustrate normal perceptual processes. • These are not errors but rather failures of perception in unusual situations.

  13. Visual Pattern Recognition • Bottom-up approaches: • Template-matching • Feature analysis • Recognition by components

  14. Template-Matching • A retinal image of an object is compared directly to stored patterns (templates). • The object is recognized as the template that gives the best match. • Used by computers to recognize patterns. • Evidence shows human recognition is more flexible than template-matching: • Size, place, orientation, shape, blurred or broken (ambiguous or degraded items easily recognized by people.

  15. Feature Analysis • Stimuli are combinations of elemental features. • Features are recognized and combined. • Features are like output of edge detectors. • Features are simpler, so problems of orientation, size, etc., can be solved. • Relationships among features are specified to define the pattern.

  16. Evidence for Feature Analysis • Confusions – people make more errors when letters presented at brief intervals contain similar features: • G misclassified: as C (21), as O (6), as B (1), as 9 (1) • When a retinal image is held constant, the parts of the object disappear: • Whole features disappear. • The remaining parts form new patterns.

  17. Object Recognition • Biederman’s recognition-by-components: • Parts of the larger object are recognized as subobjects. • Subobjects are categorized into types of geons – geometric ions. • The larger object is recognized as a pattern formed by combining geons. • Only edges are needed to recognize geons.

  18. Tests of Biederman’s Theory • Object recognition should be mediated by recognition of object components. • Two types of degraded figures presented for brief intervals: • Components (geons) missing • Line segments missing • At fast intervals (65-100 ms) subjects could not recognize components when segments were missing.

More Related