Robert E. Dewar

Rapid Comprehension of Verbal and Symbolic Traffic Sign Messages

A “same”-“different” reaction time procedure was used in two experiments to measure the times required to comprehend the meanings of projected slides of traffic signs. The results indicated that signs with symbolic messages could be understood more quickly than those with verbal messages. Visually degrading the signs resulted in a greater decrement in performance for verbal than for symbolic signs. Correlational analyses demonstrated reaction time to correlate significantly with a previously obtained measure of sign legibility taken from a moving motor vehicle on a roadway. The utility of reaction time as an index of traffic sign adequacy is discussed along with some possible practical implications of the research.

Traffic sign symbol comprehension: a cross-cultural study

The objective of this study was to evaluate the comprehension levels of highway traffic sign symbols used in different countries, to identify underlying rules that affect comprehension levels, and recommend approaches to deal with the problem. The need for such an evaluation was based on todays travel culture where people are often licensed in one country and then drive—without any further training—in another country. We compared the comprehension levels of different traffic sign symbols in four countries with moderate to high levels of motorization: Canada, Finland, Israel, and Poland. Five different driver populations were sampled in each country: novice drivers, college students, tourists, problem drivers, and older drivers. There were large differences in comprehension among specific sign messages, different countries, and different driver populations. Signs were comprehended best when they were consistent with general ergonomic guidelines for display design as they relate to spatial compatibility, conceptual compatibility, physical representation, familiarity, and standardization. Illustrations of compliance with these principles and violations of these principles are presented, and their implication for traffic safety are discussed. Specific recommendations for sign design that is compliant with ergonomic principles, and for greater international cooperation in sign symbol design are made.

REACTION TIME AS AN INDEX OF TRAFFIC SIGN PERCEPTION

Verbal reaction times to identify and to classify 20 traffic sign messages were measured under three conditions-sign alone, sign plus visual loading task, and sign plus visual loading task plus visual distraction. Similar trends were found in the three experiments: reaction times were smaller for the classification task than for the identification task, smaller for warning than for regulatory signs, and smaller for verbal than for symbolic messages. Comparison of these reaction time data with on-the-road measures of legibility distance revealed significant correlations. The correlational data add credibility to laboratory measures of reaction times as valid indices of traffic sign perception.

The slash obscures the symbol on prohibitive traffic signs

The problem of whether drivers should be told what they can do (permissive message) or what they cannot do (prohibitive message) is discussed as it relates to traffic sign symbols. A widely used version of the prohibitive message (symbol surrounded by a red ring with a slash through the symbol) was found to have limited legibility because the slash obscures the symbol. Two experiments examined the glance legibility of 15 symbols under each of four conditions-slash over symbol, slash under symbol, partial slash, and no slash. The results indicated that the glance legibility of traffic sign symbols is better when no slash or a partial slash is used to convey the prohibitive message.

Evaluation of symbolic public information signs

In a series of four experiments, symbolic representations of eight public information messages were evaluated in an attempt to identify the relative adequacy of each symbol Four versions of each message were examined using measures of legibility distance, comprehension, preference, and glance legibility. Significant positive correlations were found among the first three measures. An efficiency index was employed as an overall measure of the effectiveness of individual symbols, and recommendations were made concerning their future use.

The semantic differential as an index of traffic sign perception and comprehension

There is a need to develop and validate simple, inexpensive techniques for the evaluation of traffic sign messages. This paper examines the semantic differential (a paper-and-pencil test which measures psychological meaning) as a potential instrument for such evaluation. Two experiments are described, one relating semantic differential scores to comprehension and the other relating this index to glance legibility. The data indicate that semantic differential scores on all four factors (evaluative, activity, potency, and understandability) were highly correlated with comprehension of symbolic messages. These scores were unrelated to glance legibility of verbal messages, but two factors (evaluative and understandability) did correlate with glance legibility of symbolic messages. It was concluded that the semantic differential is a valid instrument for evaluating comprehension of symbolic sign messages and that it has advantages over other techniques.

Distribution of practice and the Müller-Lyer illusion1

Two experiments were conducted to determine the influence of distribution of practice on the decrement of the Muller-Lyer illusion. In the first experiment, Ss judged the illusion figure 100 times per session in five sessions separated by intervals of seven days. In the second, Ss judged the figure 200 limes in a single session. The data were compared with those from an earlier experiment (Dewar, 1967) in which Ss judged the figure 100 times per session in five sessions separated by 24 h. In all three experiments two configurations of the illusion were used-one with a 60° angle between the obI ique lines and one with a 120° ang Ie. The distribution of practice did not influence the decrement of the illusion for the 120° figure. The only effect of this variable was to produce a more rapid practice decrement for the 60° figure when sessions of 100 trials were separated by a 24-h intewal.

Evaluation of Prototype Highway Tourist Signs for Ontario

Information load and comprehension of new tourist signs for Ontario highways were evaluated. In a laboratory study involving 288 subjects, drivers searched for target destinations on timed sequences of slides of signs and identified whether their target was present, and, if so, its direction and distance. Performance was assessed in relation to number of names, number of signs in a sequence, arrow shapes, pictograph effectiveness, and sign organization. Signs used a letter height of 19 cm (7.5 in.). Subjects were allowed reading time equivalent to that available to drivers driving at 80 km/h (50 mph), who must time-share sign reading and vehicle control tasks. The results showed that with four or five names per sign, approximately one in eight subjects reported an incorrect direction for their target destination. Thus, a maximum of three names per sign was recommended. Results showed that a 70-degree chevron was as effective as a gerber arrow, that the number of signs in a sequence (two, three, or four) did not affect performance, and that having left followed by right destinations on a single sign resulted in equivalent performance to signs with left and right destinations on separate signs. The presence of pictographs increased the number of incorrect responses. Comprehension of 11 pictographs was assessed for 150 subjects. For 5 of 11 pictographs, comprehension was less than 85 percent.

Adaptation to displaced vision: Variations on the “prismatic-shaping” technique

Adaptation to displaced vision was measured, using three variations on Howard’s (1968) “prismatic shaping technique.” Over a series of 40 trials, a lateral displacement of 11.3 deg was introduced either gradually or suddenly. Both the amount of adaptation (negative aftereffect) and the accuracy of target localization at the completion of 40 trials were found to be directly related to the “suddenness” with which the displacement was introduced.

Evaluating pictographs using semantic differential and classification techniques

Three experiments confirm the appropriateness of the semantic differential technique as a method for measuring the extent to which various public information pictographic signs convey their intended meaning. A general classification technique, which minimizes preliminary testing, was shown to be an efficient method for measuring the similarity of meaning of pictographs to their intended lettered translation. Application of this classification technique was illustrated by examining the contribution of components of the pictographic signs to the conveyed meaning.