| One significant problem many computer users experience is that the same action can result in two or more different outcomes depending on the program mode. For example, in one mode, pressing the 'd' key can delete a file, but in another will insert the 'd' character. Mode errors can cause serious problems for software users, such as inadvertent destruction of important work, decreased productivity, and task incompletion.; A combination of qualitative and quantitative research methods was used to address three questions: What types of mode errors occur in modern human-computer interfaces, why do they occur, and how do they affect users? Eighteen undergraduate students were observed as they performed eight computer tasks using three modern 'direct manipulation systems' in usability tests. Stimulated recall interviews were conducted immediately afterwards to clarify why participants took certain actions during the tests. An observation system was then devised for coding tapes of usability tests to collect mode errors and associated behavioral patterns of the participants.; Results indicated that participants encountered 81 usability problems and exhibited 260 'problematic acts of commission and omission.' Fifty-two of the 81 usability problems were identified to be mode errors broadly classified as: (A) 'right action, wrong result'; (B) 'it isn't there where I need it'; and (C) 'it isn't there at all.' A 'source of error analysis' revealed that mode errors appear to result from eight categories of design incongruity: unaffordance, invisibility, misled expectation, unmet expectation, mismatched expectation, inconsistency unmemorability, and over-automation. The 52 mode errors resulted in consequences of 'can't find hidden function,' 'can't find unavailable function,' 'false success,' 'stuck performance,' 'inhibited performance,' and 'inefficient performance.'; Analysis of Patterns in Time (APT) indicated that type A mode errors were most likely to be associated with 'unaffordance,' often resulting in 'can't find hidden function' or 'false success.' Type B mode errors were all associated with 'mismatchced expectation' and always resulted in 'can't find hidden function.' Type C mode errors were most often associated with 'unmet expectation,' always resulting in 'can't find unavailable function.' The results of this study imply that conditions of mode errors may be considered according to user, system, and design properties. |
