The peripheral drift illusion: a motion illusion in the visual periphery

Circularly repeating patches containing sawtooth luminance gradients produce a sensation of motion when viewed in the periphery. Illusory motion is perceived in a dark-to-light direction, but only when one's gaze is directed to different locations around the stimulus, a point outside the display is fixated and the observer blinks, or when the stimulus is sequentially displayed at different locations whilst the observer fixates one point. We propose that the illusion is produced by the interaction of three factors: (i) introducing transients as a result of eye movements or blinks; (ii) differing latencies in the processing of luminance; and (iii) spatiotemporal integration of the differing luminance signals in the periphery.     

Hierarchical switching in a multi-dimensional task space

We explored shift costs for a dimensionally organized set of tasks. Task dimensions were type of judgement (numerical vs. spatial) and judgement-to-response mapping (compatible vs. incompatible). Shift costs were determined as the difference in RTs between switch trials and repetitions in a situation in which the kind of task was unpredictable. Shift costs were greatest when the type of judgement was changed. A change in the mapping increased shift costs when the type of judgement remained unchanged, but reduced shift costs when the type of judgement was changed as well. Also, response alternations produced costs when both the type of judgement and SR mapping were unchanged, but reduced shift costs otherwise. In addition to the relation between successive tasks, shift costs were modulated by the specifics of the elementary tasks. The major characteristics of the pattern of shift costs could be accounted for by the hypothesis of a dimensionally organized task space in which hierarchically organized, relative switching operations are performed that affect the highest-level task dimension at which a change is required, and all lower-level dimensions in a first step. In a second step, lower-level dimensions are switched back when no change is required, and then the selected control structure is implemented. Received: 11 December 1997 / Accepted: 6 July 1998     

Multiple cues for quantification in infancy: is number one of them?

A review and synthesis of the literature on quantification in infancy and early childhood is provided. In most current conceptualizations, early quantification is assumed to be number based. However, the extant literature provides no clear-cut evidence that infants use number to perform quantitative tasks. Instead, new research suggests that quantification is initially based on nonnumerical cues, such as area and contour length, whether or not a task involves discrete items. The authors discuss the implications of these findings with respect to early quantification and its relation to later numerical development.     

A seven-decimal table of the area (a) under the unit normal curve,for abscissae expressed in terms ofP.E.

A seven-decimal table is presented of the area under the unit normal curve, for abscissae expressed in terms of the “probable error” orPE. From the method of calculation, the partial verification by means of other tables, and the safeguards taken in the routine of computation, it is safe to consider the table reliable. Errors in previously published tables are pointed out.