Choosing specifiers: an evaluation of the basic tasks model of graphical perception.

Effect sizes obtained from 39 experiments were used to evaluate the predictions of the basic tasks model of graphical efficacy. This model predicts that performance will be attenuated with graphical displays as a function of the particular specifier, or visual dimension, used to code data values. In this review the basic tasks model predicted performance more accurately than did Tufte's data-ink principle. In addition, variability in effect sizes across studies revealed that the model was more successful at predicting performance in local (focusing) tasks than in global information synthesis tasks. Furthermore, the model was better at predicting performance in tasks requiring the use of physically present rather than remembered graphs. Further differences in effect sizes resulted from variability in the exact specifiers used in experimental graphs. Minimal differences were obtained among graphs that used position, length, or angle as specifiers. However, graphs that used area or volume to represent quantitative values were associated with consistently worse performance than found with other formats.

The perceptual interaction of graphical attributes: configurality, stimulus homogeneity, and object integration.

Researchers have proposed that graphical efficacy may be determined, in part, by the nature of the perceptual interactions that exist between attributes used to create graphical displays. One extreme type of interaction is integrality, in which two or more physical dimensions are represented as a single psychological dimension in the observer. An alternative type of interaction is configurality, in which a global emergent dimension is available to the observer in addition to the component attributes. Thirteen stimulus sets, each composed of attributes commonly used in the design of graphs, were submitted to the performance-based diagnostics of integrality and configurality. Analyses suggest a continuum of configurality among the present stimulus sets, with little evidence for integral graphical attributes. The configural pattern of results was more common when two identical dimensions were paired (homogeneous stimuli) than when two different dimensions were paired (heterogeneous stimuli). However, there was no evidence that pairs of dimensions belonging to a single object (object integration) were any more configural than dimensions belonging to different objects. Object integration was, however, consistently related to inefficient performance in tasks requiring the filtering of one of two component dimensions.

Isocapnic hypoxemia and neuropsychological functioning.

We evaluated the cognitive effects of hypoxemia independent of hypocapnia in 20 right-handed male subjects using a battery of brief neuropsychological tests. Results of a profile analysis indicated that performance during hypoxia was reliably different for Digit Symbol and Finger Tapping tests. Trend analysis demonstrated a significant linear pattern for Finger Tapping results, such that lower levels of oxygen were associated with slower rates of tapping. No significant trends were observed for Digit Symbol results. The observation of hypoxic effects on Digit Symbol and Finger Tapping tests is consistent with previous findings of neuropsychological changes secondary to hypoxia. The negative results observed for the remaining tests are inconsistent with past literature. It is likely that methodological differences contributed to these discrepancies, including previous reliance on inspired air to index hypoxemia rather than monitoring arterial oxygen saturation directly and failure to control for differences in CO2 levels during induced hypoxia. These variables should be controlled in future research.