The classification of graphical elements.

In three experiments, participants classified stimuli depicting pie charts and stacked bar graphs on two criteria: a proportion shown in the graph, and the graph's overall size (scaling). Sorting times and errors were measured. For stacked bars, performance was impaired when participants sorted on the proportion and scaling varied. No such impairment occurred for pie charts. Experiment 1 showed that varying scaling produced Garner interference in classification of proportions with stacked bars, but not pies. Experiment 2 showed that this result held when the position of the pie slice was varied; Experiment 3 results showed facilitation for particular combinations of proportion and scaling levels. In general, the results showed that proportion and scaling had an asymmetric integral relation for stacked bar graphs, but were separable dimensions for pie charts.

LCD versus CRT displays: a comparison of visual search performance for colored symbols.

Visual search performance for tactical symbols was examined with liquid-crystal (LCD) and cathode-ray tube (CRT) displays. Twenty-four adult participants (19 men, 5 women; mean age 41 years) searched for navy tactical display symbols on a map background. LCD and CRT displays of similar size and resolution (52 cm diagonal, 1280 x 1024 pixels) were used. Viewing angle (0 degrees vs. 60 degrees of azimuth), set size, target color (blue, red, or white), target presence, and search type (feature vs. conjunction) were also manipulated. Participants showed reduced sensitivity for red and blue symbols viewed 60 degrees off axis with the LCD relative to on-axis LCD, or to the CRT on or off axis. Colored symbols viewed off axis on the LCD produced longer response times in feature search and lower search efficiency in conjunction search. The results argue against the use of current LCD technology when off-axis viewing is likely and color coding is used.

Understanding bias in proportion production.

The Stevens exponent (beta) can be obtained from proportion estimation judgments using the power model. In this article, the authors extend that model to proportion production, in which the relative magnitudes of 2 stimuli are adjusted to correspond to a numeric proportion (e.g., 1/4 or .25). The model predicts that when beta < 1, small proportions are underproduced, and large proportions are overproduced, but it predicts the reverse when beta > 1, which is the opposite of the predicted patterns for estimation. Eight participants estimated and produced magnitudes and proportions with spatial volume (beta < 1; Experiment 1) and color saturation (beta > 1; Experiment 2). The model's predictions were generally supported. An extension of the model using reference points can account for multicycle patterns shown by some participants.

Bias in proportion judgments: the cyclical power model.

When participants make part-whole proportion judgments, systematic bias is commonly observed. In some studies, small proportions are overestimated and large proportions underestimated; in other studies, the reverse pattern occurs. Sometimes the bias pattern repeats cyclically with a higher frequency (e.g., overestimation of proportions less than .25 and between .5 and .75; underestimation otherwise). To account for the various bias patterns, a cyclical power model was derived from Stevens' power law. The model proposes that the amplitude of the bias pattern is determined by the Stevens exponent, beta (i.e., the stimulus continuum being judged), and that the frequency of the pattern is determined by a choice of intermediate reference points in the stimulus. When beta < 1, an over-then-under pattern is predicted; when beta > 1, the under-then-over pattern is predicted. Two experiments confirming the model's assumptions are described. A mixed-cycle version of the model is also proposed that predicts observed asymmetries in bias patterns when the set of reference points varies across trials.

The visual communication of risk.

This paper 1) provides reasons why graphics should be effective aids to communicate risk; 2) reviews the use of visuals, especially graphical displays, to communicate risk; 3) discusses issues to consider when designing graphs to communicate risk; and 4) provides suggestions for future research. Key articles and materials were obtained from MEDLINE(R) and PsychInfo(R) databases, from reference article citations, and from discussion with experts in risk communication. Research has been devoted primarily to communicating risk magnitudes. Among the various graphical displays, the risk ladder appears to be a promising tool for communicating absolute and relative risks. Preliminary evidence suggests that people understand risk information presented in histograms and pie charts. Areas that need further attention include 1) applying theoretical models to the visual communication of risk, 2) testing which graphical displays can be applied best to different risk communication tasks (e.g., which graphs best convey absolute or relative risks), 3) communicating risk uncertainty, and 4) testing whether the lay public's perceptions and understanding of risk varies by graphical format and whether the addition of graphical displays improves comprehension substantially beyond numerical or narrative translations of risk and, if so, by how much. There is a need to ascertain the extent to which graphics and other visuals enhance the public's understanding of disease risk to facilitate decision-making and behavioral change processes. Nine suggestions are provided to help achieve these ends.

Judgments of change and proportion in graphical perception.

Subjects judged change and proportion when viewing graphs in two experiments. Change was judged more quickly and accurately with line and bar graphs than with pie charts or tiered bar graphs, and this difference was larger when the rate of change was smaller. Without a graduated scale, proportion was judged more quickly and accurately with pie charts and divided bar graphs than with line or bar graphs. Perception is direct when it requires simpler or fewer mental operations; we propose that perception of change is direct with line and bar graphs, whereas perception of proportion is direct with pie charts and divided bar graphs. The results are also consistent with the proximity compatibility principle. Suggestions for improving the design of graphical displays are given.

Cervical scoliosis and kidney lesions in sheep following dosage with vitamin D.

A case of cervical deformity of lambs following dosage with vitamin D was investigated. The lesions of a scoliosis are described together with the kidney lesions. It is suggested that doses of vitamin D normally considered to be non-toxic to sheep may prove to be so under certain conditions.