Amplitude and Width Manipulations in Fitts' Paradigm: Comment on Heath et al. (2011) and Heath et al. (2016)

Heath, Weiler, Marriott, Elliott, and Binstead (2011 Heath, M., Weiler, J., Marriott, K. A., Elliott, D., &; Binstead, G. (2011). Revisiting Fitts and Peterson (1964): Width and Amplitude manipulations to the reaching environment elicit dissociable movement times. Canadian Journal of Experimental Psychology, 65, 259–268.1.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) and Heath, Samani, Tremblay, and Elliott (2016 Heath, M., Samani, A., Tremblay, L., &; Elliott, D. (2016). Fitts' theorem in oculomotor control: Dissociable movement times for amplitude and width manipulations. Journal of Motor Behavior, 48, 489–499.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) have claimed that there are dissociable movement times for amplitude and width manipulations in the Fitts' paradigm. This may to some extent be true, but the Heath et al. (2011 Heath, M., Weiler, J., Marriott, K. A., Elliott, D., &; Binstead, G. (2011). Revisiting Fitts and Peterson (1964): Width and Amplitude manipulations to the reaching environment elicit dissociable movement times. Canadian Journal of Experimental Psychology, 65, 259–268.1.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) and Heath et al. (2016 Heath, M., Samani, A., Tremblay, L., &; Elliott, D. (2016). Fitts' theorem in oculomotor control: Dissociable movement times for amplitude and width manipulations. Journal of Motor Behavior, 48, 489–499.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) data do not support that contention, as shown in this comment. It is shown that data from the research of Heath et al. is not in the range of index of difficulty where ongoing visual control would be used and hence their fits of data to Fitts' law are spurious. The data of Heath et al. (2011 Heath, M., Weiler, J., Marriott, K. A., Elliott, D., &; Binstead, G. (2011). Revisiting Fitts and Peterson (1964): Width and Amplitude manipulations to the reaching environment elicit dissociable movement times. Canadian Journal of Experimental Psychology, 65, 259–268.1.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) for arm movements and for the primary eye saccade submovements of Heath et al. (2016 Heath, M., Samani, A., Tremblay, L., &; Elliott, D. (2016). Fitts' theorem in oculomotor control: Dissociable movement times for amplitude and width manipulations. Journal of Motor Behavior, 48, 489–499.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) are well correlated by the ballistic movement time equation of Hoffmann (1981 Hoffmann, E. R. (1981). An ergonomic approach to predetermined motion time systems. Proceedings of the 9th National Conference of the Institute of Industrial Engineers, Australia, 30–47. [Google Scholar]) and Gan and Hoffmann (1988 Gan, K.-C. &; Hoffmann, E. R. (1988). Geometrical conditions for ballistic and visually controlled movements. Ergonomics, 31, 829–839.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). When the ballistic equation is used to model data for constant amplitude and constant target width conditions, the effects of the amplitude and width manipulations disappear. Other research indicates that the independent effects of movement amplitude occur due to changes in the time for the distance-covering phase of the movement.     

Reinforcing effects of caffeine in coffee and capsules.

In a residential research ward the reinforcing and subjective effects of caffeine were studied under double-blind conditions in volunteer subjects with histories of heavy coffee drinking. In Experiment 1, 6 subjects had 13 opportunities each day to self-administer either a caffeine (100 mg) or a placebo capsule for periods of 14 to 61 days. All subjects developed a clear preference for caffeine, with intake of caffeine becoming relatively stable after preference had been attained. Preference for caffeine was demonstrated whether or not preference testing was preceded by a period of 10 to 37 days of caffeine abstinence, suggesting that a recent history of heavy caffeine intake (tolerance/dependence) was not a necessary condition for caffeine to function as a reinforcer. In Experiment 2, 6 subjects had 10 opportunities each day to self-administer a cup of coffee or (on different days) a capsule, dependent upon completing a work requirement that progressively increased and then decreased over days. Each day, one of four conditions was studied: caffeinated coffee (100 mg/cup), decaffeinated coffee, caffeine capsules (100 mg/capsule), or placebo capsules. Caffeinated coffee maintained the most self-administration, significantly higher than decaffeinated coffee and placebo capsules but not different from caffeine capsules. Both decaffeinated coffee and caffeine capsules were significantly higher than placebo capsules but not different from each other. In both experiments, subject ratings of "linking" of coffee or capsules covaried with the self-administration measures. These experiments provide the clearest demonstrations to date of the reinforcing effects of caffeine in capsules and in coffee.