No abstract

The discriminability of line segments in a number of different geometric forms was examined. The procedure used was to have one of the lines within a given form drawn thinner than the other lines. The location of the thin line varied randomly within the form, and subjects were required to detect its location. Three observations were made. First, outer line elements were discriminated more accurately than inner line elements. Second, the outer-line advantage appeared to reflect an attentional strategy: By presenting inner and outer lines independently, and informing subjects in advance as to whether target lines would be in the inner or outer area of the form, the outer line advantage could be eliminated. Third, consonant with a global attentional strategy, and in opposition to any retinally tied, peripheral-to-central scanning process, an outer-line advantage was evident regardless of whether the fixation point was positioned within or outside the forms, or whether outer lines were more peripheral than inner lines.

A-C) were compared with a warm-up control condition consisting of 3 unrelated stages (E-F, G-H, A-C). The standard control condition was inferior to all other conditions and the mediated-facilitation condition was not different from the warm-up control condition. These findings were interpreted as indicating that the 3rd-stage performance in mediation and control paradigms of the type employed were determined by interlist-interference mechanisms rather than by mediational processes.

Williams and Weisstein (1978) reported that briefly presented line elements could be more accurately discerned in three-dimensional, coherent contexts than when presented alone. A series of five studies investigated this effect. The first study demonstrated that the general assumption that three-dimensional and coherent contexts are necessary conditions for demonstrating a line-in-object superiority effect is in error, and a robust effect can be demonstrated with contexts lacking coherence and depth. The remaining studies focused on a potentially more important determinant of the line-in-object effect. Evidence is presented that whether a given context facilitates, impairs, or has no effect on line detection is determined by the location of the fixation point and the amount of line detail at the fixation point. Proposals outlining processes assumed to underlie this fixation-location effect are advanced.Weisstein and Harris (1974) demonstrated an objectsuperiority effect; that is, line elements could be more accurately discerned when they were part of a unitary, three-dimensional form than when part of a flat, less unified figure. More recently, McClelland (1978) and Williams and Weisstein (1978) have presented evidence for a line-in-object superiority effect, that is, line elements can be discriminated more readily when they are part of a coherent, three-dimensional form than when presented alone in the visual field. These studies are important because they question the viability of "bottom-up" feature analyzer models that assume perceptual discrimination of primitive features such as line elements as a preliminary step in the course of pattern perception. It seems clear that the structural configuration of a form as a whole can serve to facilitate or impair detection of the individual features or elements of which the form is composed. At a minimum, these data suggest that any proposed model of pattern perception has to be complex enough to permit higher order configurational structures to influence the discrimination of lower order features.While the potential implications of these findings are substantial, before any systematic application of the findings to pattern perception theory can be made, it is necessary to determine the generality of

Possible determinants of the word-frequency effect (WFE), that is, the finding that lowfrequency (LF) words are recognized more accurately than high-frequency (HF) words, are evaluated. Three studies examined the view that, since HF words have more meanings than LF words, it is less likely that the word sense tagged at time of presentation will be accessed at time of test and a correct response will be made. To ensure the same word sense was accessed at time of presentation and time of test in the case of both HF and LF words, sentence contexts used during presentation were combined with cuing procedures at time of test. Recognition performance improved, but the WFE was unaltered even when the identical sentence context was used during presentation and test. A fourth study considered Glanzer and Bowles ' (1976) suggestion that associates of both HF and LF words tend to be HF words that are (1) likely to be activated and derivatively encoded during presentation and (2) likely to include a number of distractors from the recognition test sufficient to impair performance on HF words. Analysis of associative responses of subjects to HF and LF words, and the errors they made, support strongly such an interference-typeinterpretation of the WFE.