title: How one breaks Fitts's Law and gets away with it: Moving further and faster involves more efficient online control.
abstract: Adam, Mol, Pratt, and Fischer (2006) reported what they termed "a violation of Fitts's Law" - when participants aimed to targets in an array, movement times (MTs) to the last target location (highest index of difficulty (ID)) were shorter than predicted by Fitts's Law. Based on the results of subsequent studies in which placeholders were present either during planning and/or execution stages of the movements, it was suggested that the violation may emerge because of context-dependent changes in planning processes. The present study examined this planning explanation by conducting detailed kinematic analyses of movements. Participants performed aiming movements to sets of 3 targets in different placeholder arrays with different movement amplitudes. Consistent with previous Fitts's Law violation findings, MTs were not significantly longer for movements to the last versus middle target location. Interestingly, the pattern of peak limb velocities (typically associated with planning processes) did not mirror the changes in MTs. On the other hand, analyses of the effector's spatial variability during the movement suggested greater involvement of online control processes when the target was in the last position. Based on these results, we suggest that the Fitts' Law violation observed here occurred because of more efficient online control processes.
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario M5S 2W6, Canada; Faculty of Kinesiology and Recreation Management, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada; Health, Leisure, and Human Performance Research Institute, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada. Electronic address: cheryl.glazebrook@umanitoba.ca.
authors.forename: Cheryl M
authors.initials: CM
authors.lastname: Glazebrook
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario M5S 2W6, Canada; Department of Kinesiology, University of Maryland, College Park, SPH Building, College Park, MD 20742, United States.
authors.forename: Dovin
authors.initials: D
authors.lastname: Kiernan
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario M5S 2W6, Canada.
authors.forename: Timothy N
authors.initials: TN
authors.lastname: Welsh
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario M5S 2W6, Canada.
authors.forename: Luc
authors.initials: L
authors.lastname: Tremblay
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005121:Extremities / Q000502:physiology*; D005260:Female; D006801:Humans; D020407:Internet; D008297:Male; D009068:Movement; D009862:Online Systems; D011930:Reaction Time; D015203:Reproducibility of Results; D013997:Time Factors; D055815:Young Adult
keywords: Fitts' Law; Fitts’s Law; Kinematic analysis; Manual aiming; Reaching