The results of three experiments are reported. They were designed to substantiate the importance for skilled keying behaviour of information derived from the printed copy and the keyboard. Experiment 1 showed that consulting the copy and the keyboard during transcription constituted part of normal keying activity and that the frequency of consultation was a function of the specific demands of the task..Experiment 2, with no requirement to correct errors, and Experiment 3, with a requirement to correct errors, involved the independent masking of the copy and the keyboard as well as on unmasked control condition. Both experiments showed that an adverse effect on performance, as measured by speed and accuracy, occurred only in the keyboard masked condition. Experiment 3 revealed an additional adverse effect on performance, as measured by the reduced percentage of errors corrected, which occurred only in the copy masked condition. It was concluded that the keyboard provides ' guidance ' information, permitting the appropriate co-ordination of fingers and keys and the location of unfamiliar keys by sight, and the printed copy provides ' feedback ' information concerning the commission of errors. It is argued that the results resolve a contradiction reported in previous research and suggest that visual feedback has a continuing role even in highly practised skills, such as keying.

No abstract

This paper concerns one possible response of human factors to the need for better user interactions of computer-based systems. The paper is in two parts. Part I examines the potential for human factors to formulate engineering principles. A basic prerequisite for realizing that potential is a conception of the general design problem addressed by human factors. The problem is expressed informally as: 'to design human interactions with computers for effective working'. A conception would provide the set of related concepts which both expressed the general design problem more formally, and which might be embodied in engineering principles. Part II of the paper proposes such a conception and illustrates its concepts. It is offered as an initial and speculative step towards a conception for an engineering discipline of Human Factors.

Aggressive revascularization of the ischemic lower extremity in atherosclerotic occlusive disease by femoropopliteal (FP) and femorotibial (FT) bypass or profundaplasty (P), as indicated, has been advocated by some authors for all patients. Others have recommended primary amputation, particularly for tibial occlusive disease. To clarify this clinical dilemma, we reviewed the results of 547 procedures performed during the last 5 years: revascularization in 375 (69%) instances and below-knee amputation (BKA) in 172 (31%) cases. Bypass procedures were used in 246 cases: FP in 155 (64%) and FT in 91 (37%). Reversed autogenous saphenous vein (ASV) was used preferentially in 125 (51%) cases, whereas polytetrafluoroethylene (PTFE) was used in 121 (49%) cases. P was performed in 129 instances accompanied by inflow procedures in 92 (71%) of these cases. Cumulative limb salvage (LS) exceeded bypass patency in all categories and resulted in 2- and 5-year LS rates of 83% and 81% for FP with the use of ASV and 52% and 35% for PTFE. The LS rate for FT was 53% and 47%, respectively, for ASV and 20% and 15% for PTFE. Rest pain was successfully relieved by P in 99 cases (77%), whereas healing occurred in only 51% of cases with tissue loss. The perioperative mortality rate for revascularization was 3%; 42% of the group died during follow-up, death usually resulting from complications of atherosclerosis. Of the 172 BKAs, primary healing occurred in 80%, but the perioperative mortality rate was 13%. FP and FT bypasses are preferred procedures if ASV is available, whereas use of PTFE should be limited to FP bypasses only. Rest pain is relieved by P but tissue loss should prompt consideration for bypass. BKA should be considered in cases of severe tibial disease only in the absence of a suitable ASV, as the perioperative mortality rate is high and ultimate rehabilitation (64%) is limited.