140 likes | 141 Vues
CS 544 Human Abilities. Human Motor Capabilities.
E N D
CS 544Human Abilities Human Motor Capabilities Acknowledgement: Some of the material in these lectures is based on material prepared for similar courses by Saul Greenberg (University of Calgary), Ravin Balakrishnan (University of Toronto), James Landay (University of California at Berkeley), monica schraefel (University of Toronto), and Colin Ware (University of New Hampshire). Used with the permission of the respective original authors.
W D Example: Pointing Device Evaluation • Real task: interacting with GUI’s • pointing is fundamental • Experimental task: target acquisition • abstract, elementary, essential
Index of Difficulty (ID ) Index of Performance (IP ) = ID/MT (bits/s) W Bandwidth Throughput D Fitts’ Law (Paul Fitts, 1954) Task difficulty is analogous to information - execution interpreted as human rate of information processing
MT (secs) * * * * * * * * different way to calculate IP * * * * * * * * * * b = slope IP = 1/b * * * * * * * * * * * * a ID (bits) log2(D/W + 1)
50 years of data Reference: MacKenzie, I. Fitts’ Law as a research and design tool in human computer interaction. Human Computer Interaction, 1992, Vol. 7, pp. 91-139
What does Fitts’ law really model? Target Width Target Width Velocity (c) (a) (b) Distance
Power law of Practice • task time on nth trial follows a power law • Tn = T1 n-a, where a = .4 (empirically determined) • i.e., you get faster the more times you do it! • applies to skilled behavior (sensory & motor) • does not apply to knowledge acquisition or quality
Hick’s law • Reaction time T = a + blog2(n+1) • Where n is the number of choices • a, b empirically determined constants • log2(n+1) represents amount of information processed by human operator (in Bits) • Example: a telephone switch panel consisting of 10 buttons, any one of which may light up, prompting the operator to press the lit button. • Unequal probabilities:
Pop-up Linear Menu Pop-up Pie Menu Today Sunday Monday Tuesday Wednesday Thursday Friday Saturday Using these law’s to predict performance Which will be faster on average? • pie menu (bigger targets & less distance)?
D W D/2 D/2 D/N D/N D/N D W From targets to tunnels… • 2 goals passing • 3 goals passing • N+1 goals passing • goals passing
Fixed width tunnel Narrowing tunnel W1 W(x) W2 dx General Steering Law W(s) ds D c W Steering Law (Accot, 1997)“Beyond Fitts’ Law: Models for trajectory based HCI tasks.”Proceedings of ACM CHI 1997 Conference
Readings • MacKenzie, I. S. (1992). Movement time prediction in human-computer interfaces. (Reprinted in BGBG 483-493).