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Jeroen Smeets

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Illusions in action

Many authors have performed experiments in which subjects grasp objects in illusory surroundings. The vast majority of these studies report that illusions affect the maximum grip aperture less than they affect the perceived size. This observation has frequently been regarded as experimental evidence for separate visual-systems for perception and action. In order to make this conclusion, one assumes that the grip aperture is based on a visual estimate of the object's size. We believe that it is not, and that this is why size illusions fail to influence grip aperture.

Brentano illusion

Illusions generally do not affect all aspects of space perception in a consistent way, but mainly affect the perception of specific spatial attributes. The example in the figure shows this for the Brentano version of the Müller-Lyer illusion. The fins clearly influence the perceived extent of the green line, but leaves the perceived positions of the blue dots unaffected. Such an inconsistency applies not only to object size, but also to other spatial attributes such as position, orientation, displacement, speed, and direction of motion. Whether an illusion influences the execution of a task will therefore depend on which spatial attributes are used rather than on whether the task is perceptual or motor.

To evaluate whether illusions affect actions when they influence the relevant spatial attributes we reviewed experimental results on various tasks with inconsistent spatial processing in mind. Doing so shows that many actions are susceptible to visual illusions. We argue that the frequently reported differential effect of illusions on perceptual judgements and goal-directed action is caused by failures to ensure that the same spatial attributes are used in the two tasks. Illusions only affect those aspects of a task that are based on the spatial attributes that are affected by the illusion.

The inconsistency in the perception of the figure above (and in many other illusions) has important consequences for the nature of perception. According to Helmholtz, our perception is the result of unconscious inferences about the scene most likely to have caused the retinal image. However, the likelihood of an inconsistent scene having caused the retinal image is zero. This is a major challenge for a Helmholtzian (or Bayesian) interpretation of perception.

Publications on illusions in action

  • Smeets JBJ, Brenner E (1995) Perception and action are based on the same visual information: distinction between position and velocity. Journal of Experimental Psychology: Human Perception and Performance 21:19-31 (reprint)
  • Smeets JBJ, Brenner E (1995) Prediction of a moving target's position in fast goal-directed action. Biological Cybernetics 73:519-528 (reprint).
  • Brenner E, Smeets JBJ (1996) Size illusion influences how we lift but not how we grasp an object. Experimental Brain Research, 111:473-476 (reprint).
  • Smeets JBJ, Brenner E (2001) Perception and action are inseparable. Ecological Psychology 13:163-166 (reprint).
  • Smeets JBJ, Brenner E (2001) Action beyond our grasp. Trends in Cognitive Sciences, 5:287 (reprint).
  • Smeets JBJ, Brenner E. (2001) The absence of representations causes inconsistencies in visual perception. Behavioral and Brain Sciences, 24:1006 (reprint).
  • de Grave DDJ, Smeets JBJ, Brenner E (2002) Ecological and constructivist approaches and the influence of ilusions. Behavioural and Brain Sciences, 25:103-104 (reprint).
  • de Grave DDJ, Brenner E, Smeets JBJ. (2002) Are the original Roelofs effect and the induced Roelofs effect caused by the same shift in straight ahead? Vision Research, 42:2279-2285 (reprint).
  • Smeets JBJ, Brenner E, de Grave DDJ, Cuijpers RH (2002) Illusions in action: consequences of inconsistent processing of spatial attributes. (Review) Experimental Brain Research, 147:135-144 (reprint).
  • López-Moliner J, Smeets JBJ, Brenner E. (2003) Comparing the sensitivity of manual pursuit and of perceptual judgements to pictorial depth effects. Psychological Science, 14:232-236 (reprint).
  • Smeets JBJ, Glover S, Brenner E. Modeling the time-dependent effect of the Ebbinghaus illusion on grasping. (2003) Spatial Vision, 16:311-324 (reprint).
  • López-Moliner J, Smeets JBJ, Brenner E (2003) Similar effects of a motion-in-depth illusion on manual tracking and perceptual judgements. Experimental Brain Research, 151:553-556 (reprint).
  • Brouwer AM, Brenner E, Smeets JBJ (2004) Using the same information for planning and control is compatible with the dynamic illusion effect. Behavioural and Brain Sciences 27:28-29 (reprint).
  • de Grave DDJ, Brenner E, Smeets JBJ (2004) Illusions as a tool to study the coding of pointing movements. Experimental Brain Research 155:56-62 (reprint).
  • de Grave DDJ, Brenner E, Smeets JBJ (2004) An apparent compression cannot explain the difference between the original and the induced Roelofs effect. Vision Research 44,1031-1032 (reprint).
  • Smeets JBJ, Brenner E (2004) Curved movement paths and the Hering illusion: positions or directions? Visual Cognition, 11:255-274 (reprint).
  • de Grave DDJ, Biegstraaten M, Smeets JBJ, Brenner E. (2005) Effects of the Ebbinghaus figure on grasping are not due to misjudged size Experimental Brain Research 163:58-64 (reprint)
  • de Grave DDJ, Smeets JBJ, Brenner E (2006) Why are saccades influenced by the Brentano illusion? Experimental Brain Research 175:177-182 (repint).
  • Smeets JBJ, Brenner E (2006) Ten years of illusions. Journal of Experimental Psychology: Human Perception and Performance 32:1501-1504 (reprint)
  • Biegstraaten M, de Grave DDJ, Smeets JBJ, Brenner E. (2007) Grasping the Müller-Lyer illusion: not a change in length. Experimental Brain Research 176:497–503 (reprint).
  • Brenner E, Smeets JBJ (2007) Insights about seeing. Cortex 43:271-274 (reprint)
  • Smeets JBJ, Brenner E (2008) Why we don’t mind to be inconsistent. In: Handbook of Cognitive Science – An Embodied Approach (Calvo, P. & Gomila, T., ed) Elsevier. pp 207-217 (reprint)
  • de Grave DDJ, Brenner E, Smeets JBJ (2009) The Brentano illusion influences goal-directed movements of the left and right hand to the same extent. Experimental Brain Research 193:421–427 (reprint)
  • Smeets JBJ, Sousa R, Brenner E (2009) Illusions can warp visual space. Perception 38:1467-1480 (reprint, DOI)
  • Smeets JBJ, Brenner E (2010) Vision for action is not veridical. Cognitive Neuroscience, 1:69 (reprint)
  • Plaisier, M.A., Smeets, J.B.J. (2012) Mass Is All That Matters in the Size–Weight Illusion. PLoS One, 7(8): e42518 (reprint, DOI)
  • Matziridi, M., Brenner, E., Smeets, J.B.J. (2013). Is Mislocalization during saccades related to the position of the saccade target within the image or to the gaze position at the end of the saccade? PLoS One, 8(4): e62436 (reprint, DOI)

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