Attentional Tracking in the Perception of Apparent Motion: Evidence from Sequential Blanking Displays

Perception of sequential blanking displays was studied in a series of three experiments investigating factors that influence whether “shadow motion” or “item motion” is seen in a display. In addition to the duration of the blanking interval (BI) itself, three other such factors were identified: the eccentricity at which the display is viewed, the spacing of items in the display, and the type of motion that subjects are instructed to try to see. It is argued that these and other previously reported results are explicable without the need to invoke any kind of visual integration period. Instead, they are interpreted in terms of a first-order system of automatic luminance detectors and a second-order tracking system involving both voluntary and involuntary attention. The relationship of these findings to other recent work in apparent motion and visual attention and to other bistable motion displays is discussed.     

Selective attention, visual laterality, awareness, and perceiving the meaning of parafoveally presented words

Four experiments are reported investigating the effect of selective attention on the semantic encoding of parafoveally presented words. In Experiments 1 and 2 a right visual field (RVF) performance bias was found when subjects attended to words that could appear either left or right of centre (attend-side condition). When subjects attended centrally and ignored lateral distractor words (attendcentre condition) there was an inhibitory effect of word meaning from left visual field (LVF) distractors. Both inhibitory and facilitatory effects of semantic category were observed from unattended words in Experiments 3 and 4. The pattern of effects depended upon the direction of spatial bias in an attend-side condition. Both kinds of effect occurred even for subjects who were unable to make consciously directed semantic category decisions to words at the same eccentricity (4°) and exposure time (15 msec) as ignored distractors in the attend-centre condition. Implications of these findings for theories of selective attention, for the issue of semantic encoding independent of conscious awareness, and for theories of the relationship between lateral performance biases and functional hemispheric asymmetry are discussed.     

Parsing of algebraic expressions by experienced users of mathematics

The present study investigates how experienced users of mathematics parse algebraic expressions. The main issues examined are the order in which the symbols in an expression are scanned and the duration of fixation. Two experiments tracked the order in which the symbols of an expression were scanned. The results were analysed using Markov Chain models of the scanpath data and provided strong support for the hypothesised scanning order: a left-to-right, top-to-bottom syntax-based scanning order. Length of fixation was also analysed in the first experiment. When reading text, readers pause significantly longer at the end of clauses and sentences. A similar pattern was found for mathematical expressions: Symbols at the end of a phrasal constituent were fixated upon for significantly longer than symbols at the start or middle of the phrasal constituent. These results suggest that the parsing of algebraic expressions has marked similarities with the way in which sentences of natural language are processed and reinforces the importance of syntax in their comprehension.