On the spatial distribution of visual attention

An implication of the data analysis and presentation of Podgorny and Shepard (1983) is that subjects are able to attend simultaneously to more than one square of a grid display when the squares are separated by unattended areas: Attention to such nonunitary areas produces similar benefits as attention to unitary areas. These benefits are reflected in reaction times (RTs), which were reported by Podgorny and Shepard (1983) as being related to a measure of spatial dispersion (compactness) of the attended areas, but this measure does not signify whether these areas are unitary or not. A reanalysis of part of Podgorny and Shepard's (1983) data shows that RTs to attended and unattended squares are almost identical when the attended areas are nonunitary. This reanalysis also shows that RTs are related to compactness for unitary attended areas but that this relation breaks down when attention is focused on nonunitary areas. In addition, Podgorny and Shepard's (1983) data are presented in a way that demonstrates the importance of the actual grid location of probes on RTs. The failure of compactness to reflect these aspects of the spatial nature of attention suggests that this metric is deficient when applied to the study of the spatial determinants of attention.