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.
Visual Illusions Depend on experience. Influenced by culture. Illustrate normal perceptual processes. These are not errors but rather failures of perception in unusual situations.
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.
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.
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.
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.
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.
Speech Recognition The physical speech signal is not broken up into parts that correspond to recognizable units of speech. Undiminished sound energy at word boundaries – gaps are illusory. Cessation of speech energy in the middle of words. Word boundaries cannot be heard in an unfamiliar language.
Phoneme Perception No one-to-one letter-to-sound correspondence. Speech is continuous – phonemes are not discrete (separate) but run together. Speakers vary in how they produce the same phoneme. Coarticulation – phonemes overlap. The sound produced depends on the sound immediately preceding it.
Feature Analysis of Speech Features of phonemes appear to be: Consonantal feature (consonant vs vowel). Voicing – do vocal cords vibrate or not. Place of articulation – where the vocal track is constricted (where is tongue placed). The phoneme heard by listeners changes as you vary these features. Sounds with similar features are confused.
Categorical Perception For speech, perception does not change continuously but abruptly at a category boundary. Categorical perception – failure to perceive gradations among stimuli within a category. Pairs of [b]’s or [p]’s sound alike despite differing in voice-onset times.
Two Views of Categorical Perception Weak view – stimuli are grouped into recognizable categories. Strong view – we cannot discriminate among items within such a category. Massaro – people can discriminate within category but have a bias to same items are the same despite differences. Category boundaries can be shifted by fatiguing the feature detectors.