Trends in Cognitive Sciences
Volume 5, Issue 11, 1 November 2001, Pages 457-459
Journal home page for Trends in Cognitive Sciences

Research update
Action does not resist visual illusions

https://doi.org/10.1016/S1364-6613(00)01772-1Get rights and content

Abstract

Recent TICS articles1, 2 discussed the psychophysical evidence in favor of Goodale and Milner's action vs. perception hypothesis3. Carey argued that most of the studies investigating the effects of visual illusions on grasping can be reconciled with the notion that the action system resists visual illusions1. Bruno suggested a new interpretation of the action vs. perception hypothesis in order to incorporate most of the empirical findings2. Here, I argue that action does not resist visual illusions. Even more, the effects on the motor system seem to be comparable to the effects on the perceptual system. This challenges the action vs. perception hypothesis in its current form.

Section snippets

Standard perceptual measures provide no evidence for a smaller motor illusion

The perceptual effects of visual illusions have been assessed in different ways. In Table 1, I distinguish between standard perceptual measures and non-standard perceptual measures. Standard perceptual measures are usually used in the investigation of visual illusions. For example, participants adjust the size of a comparison stimulus to match the size of a target stimulus.

Aglioti et al. (Ref. 4, and replicated in Refs 5, 9) found that the Titchener/Ebbinghaus illusion affected standard

Non-standard perceptual measures show larger illusion effects than both perception and action

A number of studies used non-standard perceptual measures. Usually, participants estimated target size by opening index finger and thumb, either seeing or not seeing their hand and the stimulus during performance of the task5, 8, 12, 13, 14, 16. I see two problems with these non-standard perceptual measures (see also Ref. 17). First, it is unclear whether these measures can be interpreted as perceptual measures. As Bruno pointed out2, it is difficult to find a priori criteria for classifying

Is it possible to reconcile the action vs. perception hypothesis with these data?

There have been different attempts to reconcile the action vs. perception hypothesis with the finding of equal motor and perceptual illusions in the Titchener/Ebbinghaus display6, 7. Some authors have argued that the motor illusion might be generated in the motor system independently of the perceptual illusion1, 8, 18, 19. This could be the case if the motor system treated the context circles as potential obstacles for the fingers and tried to avoid them. In my opinion, this is an important

Conclusions

At first, the finding of Aglioti et al. that the motor system largely resisted the Titchener/Ebbinghaus illusion seemed to provide convincing evidence for the Milner and Goodale action vs. perception hypothesis. Today, this finding is in doubt and the accumulated evidence suggests that the effects of the illusion on grasping might well be similar to the effects on perception. As directions for future research, I suggest that more attention be paid to the problem of matching the task demands of

Acknowledgements

This work was supported by the grant FA 119/15–3 from the Deutsche Forschungsgemeinschaft (DFG) and by the Max Planck Society.

References (23)

  • V.H. Franz

    Grasping visual illusions: no evidence for a dissociation between perception and action

    Psychol. Sci.

    (2000)
  • Cited by (194)

    • The target as an obstacle: Grasping an object at different heights

      2018, Human Movement Science
      Citation Excerpt :

      They used five differently shaped target objects with the same maximal width, height, and depth. Verheij et al. (2014) showed that the effect of target object shape on MGA could better be explained by considering the target object as an obstacle at positions other than the envisioned goal positions for the digits, than by the desired precision of the digits’ final positions (Smeets & Brenner, 1999), perceived width of the target object (Franz, 2001; Franz, Fahle, Bülthoff, & Gegenfurtner, 2001; Franz, Gegenfurtner, Bülthoff, & Fahle, 2000) or the perceived volume of the target object (Borchers et al., 2014). Another movement parameter that is influenced by obstacles is the movement time (MT): obstacles in general lead to a longer MT (Biegstraaten, Smeets, & Brenner, 2003; Mon-Williams et al., 2001).

    View all citing articles on Scopus
    View full text