Dynamic effects of the Ebbinghaus illusion in grasping: Support for a planning/control model of action

Abstract

The distinctionbetween the premovement planning of an action and its on-line control has a long history (e.g., Jeannerod, 1988;Keele & Posner, 1968;Woodworth, 1899). Here, we demonstrate that the earlier portions of a grasping movement are more affected by the Ebbinghaus illusion than are the latter portions. These results provide further support for a planning/control model (Glover, 2001;Glover & Dixon, 2001a, 2001b, 2001d in which planning is more susceptible to illusions than control. The results do not support a perception/action model (e.g., Aglioti, DeSouza, & Goodale, 1995;Bridgeman, 1999;Bridgeman, Peery, & Anand, 1997;Goodale & Milner, 1992;Milner & Goodale, 1995), in which both planning and control are thought to be less susceptible to illusions than are perceptions.Woodworth (1899) was the first to demonstrate the distinctionbetween the premovement planning and the on-line control of action. Woodworth found that when participants were asked to draw lines of particular lengths, they required sufficient time to correct the actions on line. For example, accuracy was worse at a drawing rate of 400 msec per line than at slower rates. Furthermore, if the linedrawing task was done without vision, participants' performance at all speeds was just as poor as when the task was done quickly with vision. Woodworth reasoned from this that actions were composed of two stages: an "initial impulse" stage that reflected the premovement planning of the action and a subsequent "current control" stage that reflected the on-line correction of an action via feedback mechanisms.Since Woodworth's (1899) seminal study, much research has gone into characterizingthese two stages of action (e.g., Abrams & Pratt, 1993;Elliot, Binsted, & Heath, 1999;Flash & Henis, 1991;Keele & Posner, 1968;Khan, Franks, & Goodman, 1998;Meyer, Abrams, Kornblum, Wright, & Smith, 1988;Pratt & Abrams, 1996), and some distinctions between the two stages have been elucidated. For example, planning appears to be a relatively slow and deliberate process. The minimum time required to initiatea movement has been found to be around 250 msec (Stark, 1968). Conversely, on-line control appears to operate relatively quickly. In contrast to the 400-msec lag between planning and control stages hypothesized by Woodworth on the basis of his original study, the benefits of visual and proprioceptive feedback during on-line control have more recently been found to occur in as little as 70-150 msec (e.g., Evarts & Vaughn, 1978;Lee & Tatton, 1975;Smeets, Erkelens, & van der Gon, 1990;Zelaznik, Hawkins, & Kisselburgh, 1983).We have hypothesized that another difference between planning and control may be how each is affected by context-induced visual illusions. In the planning/control model (Glover, 2001;Glover & Dixon, 2001a, 2001b, 2001d, context-induced illusions affect the planning process, but not the on-line control process. We use the term context-inducedto refer to distortions that arise owing to the visual context surrounding the target, as opposed to those that re...

Planning versus online control: dynamic illusion effects in grasping?

“…Usually (but not always) this will result in an underestimation of the variability for the corrected illusion effects (and, consequently, in liberal statistical tests). Unfortunately, this problem is present in the study of Glover and Dixon (2002). As an example, we calculated the corrected illusion effects in the same way as Glover and Dixon (2002) did.…”

“…Unfortunately, this problem is present in the study of Glover and Dixon (2002). As an example, we calculated the corrected illusion effects in the same way as Glover and Dixon (2002) did. This results in corrected illusion effects of: 1.32 ± 0.34 for t = 100%, 1.23 ± 0.34 for t = 75%, 1.27 ± 0.37 for t = 50%, 1.14 ± 0.78 for t = 25%, and 21.51 ± 11.44 for t = 0%.…”

“…Time points after the maximum grip aperture were not included in the analysis, because here the fingers are already very close to the target and quite often one or the other finger already touches the target object, which would contaminate the data. To be maximally comparable to previous studies, the same criterion for movement onset was used as in the study of Glover and Dixon (2002): Movement onset was defined as the first time when the velocity of the thumb exceeded a value of 0.1 m/sec. Maximum grip aperture was defined as the maximum of the aperture values between onset of the movement and reaching the disc.…”

Effect of structuring the workspace on cognitive and sensorimotor distance estimation: No dissociation between perception and action

“…One could wonder, moreover, what would be the benefit for the visual system of having two independent pathways dealing with identical spatial processing. This also rules out the possibility that context information influenced motor planning but not control process, allowing on-line minimization of the spatial error of the movement (the planning-control model; Glover, 2004;Glover & Dixon, 2002). An alternative would be to consider that the processing of context information remains the prerogative of the ventral stream, which can influence the sensorimotor system in some circumstances.…”

Visual Processing in the Action-Oriented Brain

“…One of the pieces of behavioural evidence for the PCM was a careful examination of the unfolding movement during actions towards visual illusions. Glover and Dixon [13] showed that the effect of an illusion on grip aperture was stronger at the start of the movement and diminished as the movement progressed, potentially indicating that movement planning and movement control were drawing upon different representations of the target and its environment.…”