Central sources of visual masking: Indexing structures supporting seeing at a single,brief glance

Summary When two briefly exposed, spatially overlapping visual fields are presented dichoptically, the identifiability of the first field is a J-shaped function of the interval separating their onsets. Three distinct sources of central masking are inferred from the selective influence of variables at different onset asynchronies. In integration through common synthesis, two fields presented at or near simultaneous onset yield one iconic representation. The distinctiveness of this source is inferred from the selective influence of eye dominance at and near simultaneous onset. At longer onset asynchronies, the selective influence of variables such as mask contrast and degree of contour overlap imply a second source of masking. This source was identified with the inhibition of sustained channels by transient channels reported elsewhere. Interchannel inhibition is proposed to affect the fidelity of the iconic representation, but here the imprecision is due to loss of form-relevant information on the first field. At yet longer onset asynchronies, where the fields are phenomenally separate, a third set of variables (e.g., words vs. nonwords and left vs. right visual fields) show their influence. These effects are taken as evidence of a replacement principle: the iconic representation of the second field directs attention from that of the first field. Here, first-field identifiability is constrained by time rather than by impoverished data.In a final series of experiments, central three-field interactions are demonstrated. A field, inserted into the temporal gap between two fields, is perceptually impaired even though it is separated from the first and third fields by intervals at which, individually, neither field is an effective mask. This second-field depression is accompanied by a first-field enhancement. The three sources of central masking are hard pressed to account for the three-field effects.     

Conservation training in four-year-old children

In Experiment 1 two training procedures were used to teach four-year-olds to conserve. Verbal rule instruction consisted of providing verbal rules and demonstrations of the operations referred to by the rules. Feedback consisted of providing verbal feedback contingent upon the children's responses. One week after training on conservation of number and length the children were given a posttest which included tests of conservation of number, length, and mass. Children who were given verbal rule instruction conserved significantly more on the number and length posttest problems than children who were not. However, this learning did not transfer to the mass problems, possibly because mass is not naturally acquired until some time after conservation of number and length. The feedback training procedure had no effect on conservation performance. In Experiment 2, the verbal rule instruction procedure was used to train four-year-olds on conservation of length and mass. One week after training the children were tested on both conservation of number, which is typically acquired before length and mass, and conservation of weight, which is typically acquired after length and mass, as well as on conservation of length and mass. Children who were given training conserved more on all four types of problems than children in the control group.