Identifying Raised-Line Drawings by Touch: A Hard but Not Impossible Task

Drawings are usually visual, but may also be tactile, that is, perceptible through the fingers (Eriksson, 1988). In the latter case, they may be extremely useful to people who are blind (Kennedy, 1993). Identifying raisedline drawings of everyday objects by touch is far from easy, however. Whether tactile drawings can be interpreted without recourse to visual experience and imagery has evoked different views. This issue is central to the debate between Kennedy (1993; the optimistic view) and Lederman, Klatzky, Chataway, and Summers (1990; the pessimistic view) on the perception of tactile pictures. This debate has not been resolved, insofar as studies have yielded inconsistent results regarding the ease with which individuals respond to tactile picture-naming tasks. The topic of tangible drawings for individuals who are blind is an important one to the field of visual impairment. However, it has not been addressed so far in a literature review. In this article, we review the selected literature on tactile picture naming and provide a quantitative look at this literature by presenting results related to accuracy (percentage of correct naming). We attempt to identify the factors that influence accurate picture naming when identifying raised-line drawings. CORPUS OF STUDIES We selected studies that asked individuals who are blind and those who are sighted to identify as quickly and as accurately as possible a set of tactile drawings depicting common objects. A search of scientific databases (PubMed, Science Direct) yielded 16 articles that were published over the past 30 years that matched our inclusion criteria: publication in a journal, the use of raised-line drawings of everyday objects as stimuli, the use of a tactile picture-naming task (requiring both speed and accuracy), participants who were blind and those who were sighted, and the reporting of mean accuracy measures. Studies using tactile picture-matching tasks, multiple-choice procedures, or tactile graphics and maps were excluded. The main findings obtained in each study are summarized in Table 1. VARIABLES OF INTEREST A detailed examination of the corpus (see Table 1) identified five known variables whose effects were assessed in the literature (A: participants' visual status, B: type of picture, C: size of picture, D: information given for the task, and E: mode of exploration). Five additional parameters on which the studies differed, but whose effects have not been assessed in the literature, were documented (F: picture set, G: number of pictures, H: type of paper, I: exploration time, and J: number of participants). These parameters are worth considering because they may influence picture-naming accuracy. A total of 46 measures of mean accuracy were obtained (these means were obtained from the original articles). These measures could be compared together to the extent that all studies used a picture-naming task, leading to accuracy measures (percentage of correct naming). Overall, the mean accuracy was 42%, with wide variations across the studies (SD: 21, range: 9-85). EFFECTS OF KNOWN VARIABLES Studies that assessed the effect of visual status on accuracy of identification of raisedline drawings provided inconsistent findings. Some showed that participants with late-onset blindness outperformed participants with early-onset blindness and those who were sighted (study 2) or participants with early-onset blindness only (study 11), whereas others showed that participants who were sighted outperformed participants with early-onset blindness (study 3) or the reverse (study 7). These inconsistencies may have partly been due to methodological differences of the various studies. In the whole corpus, the performance of participants who were blind ranged from 9% to 82%, and the performance of participants who were sighted ranged from 9% to 85%. With respect to the type of picture, there was converging evidence that three-dimensional, visually realistic pictures yielded lower accuracy scores than did pictures without depth information (two-dimensional pictures or Texyform pictures involving a tactile depiction code) (studies 3, 10, 11, and 16). …