Analysis of RhoA-binding proteins reveals an interaction domain conserved in heterotrimeric G protein beta subunits and the yeast response regulator protein Skn7

To identify potential RhoA effector proteins, we conducted a two-hybrid screen for cDNAs encoding proteins that interact with a Gal4-RhoA.V14 fusion protein. In addition to the RhoA effector ROCK-I we identified cDNAs encoding Kinectin, mDia2 (a p140 mDia-related protein), and the guanine nucleotide exchange factor, mNET1. ROCK-I, Kinectin, and mDia2 can bind the wild type forms of both RhoA and Cdc42 in a GTP-dependent manner in vitro. Comparison of the ROCK-I and Kinectin sequences revealed a short region of sequence homology that is both required for interaction in the two-hybrid assay and sufficient for weak interaction in vitro. Sequences related to the ROCK-I/Kinectin sequence homology are present in heterotrimeric G protein beta subunits and in the Saccharomyces cerevisiae Skn7 protein. We show that beta2 and Skn7 can interact with mammalian RhoA and Cdc42 and yeast Rho1, both in vivo and in vitro. Functional assays in yeast suggest that the Skn7 ROCK-I/Kinectin homology region is required for its function in vivo.     

Combining information: Probability summation and probability averaging in detection and discrimination.

Detection may improve if a stimulus offers 2 cues rather than 1. This is sometimes attributed to probability summation of independent detections, which provides an especially simple model for sensory information combination. However, this model assumes a strong bias toward the positive response, which is not appropriate for discrimination. The probability summation model is here extended to apply to discrimination and to allow different degrees of summation, ranging from complete through partial to probability averaging, and the use of this model is illustrated for the method of constant stimuli. It allows performance based on independent decisions to be distinguished from performance (e.g., integration) that is better than summation can explain. Models for the discrimination of complex stimuli may provide a tool for studying the development of expertise in areas where this involves a perceptual component, such as clinical judgment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The line–motion illusion: Attention or impletion?

When a brief lateral cue precedes an instantaneously presented horizontal line, observers report a sensation of motion in the line propagating from the cued end toward the uncued end. This illusion has been described as a measure of the facilitatory effects of a visual attention gradient (O. Hikosaka, S. Miyauchi, & S. Shimojo, 1993a). Evidence in the present study favors, instead, an account in which the illusion is the result of an impletion process that fills in interpolated events after the cue and the line are linked as successive states of a single object in apparent motion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

There are two types of psychometric function: A theory of cue combination in the processing of complex stimuli with implications for categorical perception.

Psychometric functions are customarily fitted using normal distribution functions. However, categorical perception identification tasks give functions that are more sigmoid than the normal distribution (M. Treisman, A. Faulkner, P. L. N. Naish, & B. S. Rosner, see record 1995-42700-001). This can be explained by a theory of discrimination, cue combination theory (CCT), presented here. This theory assumes that complex stimuli (e.g., speech sounds) are composed of components or cues that vary in informativeness. The decision mechanisms sample individual cue dimensions and combine the information from each. The model generates a normal psychometric function if all cues sampled are informative. If not, the function becomes more sigmoid. CCT offers accounts of discrimination (categorical and continuous) and sensory reaction times, adaptation, sequential effects, contextual effects, trading relations, speed and accuracy, perceptual learning, and the separable-integral distinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicit and explicit memory for visual patterns.

The article reports an investigation of implicit and explicit memory for novel, visual patterns. Implicit memory was assessed by a speeded perception task, and explicit memory by a four-alternative, forced-choice recognition task. Tests were given either immediately after testing or 7 days later. The results suggest that a single exposure of a novel, nonverbal stimulus is sufficient to establish a representation in memory that is capable of supporting long-lived perceptual priming. In contrast, recognition memory showed significant loss over the same delay. Performance measures in the two tasks showed stochastic independence on the first trial after a single exposure to each pattern. Finally, a specific occurrence of a previously studied item could be retrieved from explicit memory but did not affect the accuracy of perception in the implicit memory test. The results extend the domain of experimental dissociations between explicit and implicit memory to include novel, nonverbal stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature analysis in early vision: Evidence from search asymmetries.

A series of search experiments tested detection of targets distinguished from the distractors by differences on a single dimension. Our aim was to use the pattern of search latencies to infer which features are coded automatically in early vision. For each of 12 different dimensions, one or more pairs of contrasting stimuli were tested. Each member of a pair played the role of target in one condition and the role of distractor in the other condition. Targets defined by larger values on the quantitative dimensions of length, number, and contrast, by line curvature, by misaligned orientation, and by values that deviated from a standard or prototypical color or shape were detected easily, whereas targets defined by smaller values on the quantitative dimensions, by straightness, by frame-aligned orientation, and by prototypical colors or shapes required slow and apparently serial search. We interpret the results as evidence that focused attention to single items or to groups is required to reduce background activity when the Weber fraction distinguishing the pooled feature activity with displays containing a target and with displays containing only distractors is too small to allow reliable discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)