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J S Lappin

Publications and source records attributed to J S Lappin.

33 records · Page 2Linked to original sources
PubMed1981

The perceptual coherence of moving visual patterns.

Two experiments evaluated the detectability of coherent motion as a function of the coherence and relative direction of motion of the background in which it occurred. The stimulus patterns consisted of sequential frames of randomly positioned dots that could be displaced relative to each other; their coherence was defined by the correlation between positions of dots in successive frames. When all of the correlated components were displaced in the same direction, the detectability of coherent motion of any given component was approximately independent of the coherence of the remainder of the pattern, and the perceived coherence of the whole pattern was proportional to its statistical coherence. Such performance is characteristic of linear system. When two superimposed lattices were displaced in opposite directioins, however, they were competitive in that increasing coherence of one direction decreased the detectability of coherent motion in the opposite direction. The latter results as well as those of other experiments indicate that the visual system is nonlinear. In general, the perceived coherence reflects the coherence of the stimulus patterns.

Form Perception↗
PubMed1981

Visual detection of multi-letter patterns.

This study addressed two basic questions about the detection of multi-letter patterns: (a) How is the detection of a multi-letter pattern related to the detection of its individual components? (b) How is the detection of a sequence of letters influenced by the observer's familiarity with that sequence? In three experiments observers searched for one-, two-, or three letter patterns embedded in a rapid series of multiple six-letter frames. In Experiment 1, unfamiliar two-letter patterns were detected more accurately than their one-letter components. This two-letter advantage reflects the fact that in an array of fixed size, larger target stimuli contain more information and are easier to discriminate from nontarget alternatives. Quantitative analyses indicated that observers combine information not decisions, about the component letters in a pattern. In Experiment 2, with statistical and physical properties equated, a familiar three-letter pattern (i.e., CAT) was detected more accurately than its unfamiliar anagram (i.e., TCA). This word advantage in word (not letter) detection persisted even after extensive practice and was uninfluenced by the lexical character of distractor items. In Experiment 3, words (e.g., FIB), pronounceable non words (e.g., FIF(, and familiar acronyms (e.g., FBI) were detected more readily than unfamiliar items (e.g., IBF). Thus both orthographic knowledge and familiarity with specific sequences can facilitate perceptual processing in "word" detection.

Cognition↗
PubMed1980

Minimal conditions for the visual detection of structure and motion in three dimensions.

Human observers detected the global three-dimensional organization of visual patterns consisting of only two successive frames of randomly positioned dots, corresponding to projections of a rotating sphere. A perfectly coherent sphere yielded a stable perceptual organization that was detected more accurately than other slightly less organized patterns.

Humans↗
PubMed1975

On the relation between time and space in the visual discrimination of velocity.

Is the perception of velocity determined by the prior discrimination of spatial and temporal distances? Two experiments sought to answer this question by comparing the discriminabilities of moving stimuli varied in spatial extent, temporal duration, or in redundant combinations of both variables. The subject's task was to identify which of two alternative stimuli was presented on each trial. A set of four stimuli was constructed from two values of spatial extent and two values of temporal duration. Separate conditions required discrimination of each of the six possible pairs of these stimuli. Experiment 1 examined continuous motion and Experiment 2 examined apparent motion for stimuli with short (50 versus 65 msec) and with long (500 versus 650 msec) interstimulus intervals. With continuous motion and with good apparent motion (short intervals), the discrimination between the different-velocity bivariate pairs was too accurate to be attributed only to discriminations of the spatial and temporal extents of the motion. This did not occur with poor apparent motion. Evidently, time and space are perceptually related.

Adolescent↗