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Psychology Presentations Psychology Department

2010

Lifting without Seeing: The Role of Vision inPerceiving and Acting upon the Size‐weight IllusionGavin BuckinghamThe University of Western Ontario, gbucking@uwo.ca

Melvyn A. GoodaleThe University of Western Ontario, mgoodale@uwo.ca

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Citation of this paper:Buckingham, Gavin and Goodale, Melvyn A., "Lifting without Seeing: The Role of Vision in Perceiving and Acting upon theSize‐weight Illusion" (2010). Psychology Presentations. 41.https://ir.lib.uwo.ca/psychologypres/41

Lifting without seeingThe role of vision in perceiving and acting upon the size‐weight illusion

Gavin Buckingham & Melvyn A. GoodaleCentre for Brain and Mind, University of Western Ontario, Canada; 

IntroductionOur expectations of an object’s heaviness not only drive our fingertip forces, but also our perceptionof heaviness. This effect is highlighted by the classic size‐weight illusion (SWI), where different‐sizedobjects of identical mass feel different weights (Charpentier, 1891) long after any initial errors in the

Email: gbucking@uwo.ca; Web: http://publish.uwo.ca/~gbucking

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application of fingertip forces have been corrected (Flanagan & Beltzner, 2000).

Here, we examined whether our expectations about the weight of an upcoming lift are sufficient toinduce the SWI in a single wooden cube when lifted without visual feedback, by varying the size ofthe object seen prior to the lift during a brief preview.

We also measured fingertip forces during lifts of this cube, in order to determine whether theexpectations of heaviness associated with the previewed object would affect the application of gripand load forces We contrasted perceptual and kinetic data with those from a full vision SWI task 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

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and load forces. We contrasted perceptual and kinetic data with those from a full‐vision SWI task.

Materials & methodsFull vision task: Participants sat in front of a table wearing closed PLATO shutter goggles. The gogglesopened at the same time as an auditory go cue, at which point participants reached out and lifted oneof the identically‐weighted (700g) SWI cubes (A) with their thumb and index finger on the forcet d h dl h ld it l ft f 3 d d t d it t th t ti iti P ti i t

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transducer handle, held it aloft for 3 seconds, and returned it to the starting position. Participantsthen gave a numerical magnitude estimation of how heavy the cube felt.

No vision task: The shutter goggles opened for 1 second, giving participants a brief view of the (small,medium, or large) cube on the table. The goggles then closed, at which point the experimenterreplaced the ‘seen cube’ with the medium‐sized cube ‐ the only object lifted by participants in the no‐vision task. The participants, who were not aware that this substitution had taken place, then liftedthe medium‐sized cube and rated its heaviness, while the goggles remained closed (B).

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the medium sized cube and rated its heaviness, while the goggles remained closed (B).

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The small 700g cube felt heavierthan the large 700g cube.

Grip and load force rates scaledfrom the expected weight to thet l ( d id ti l) f

Seeing the small cube made themedium‐sized cube feel heavier thanit felt after seeing the large cube.

Grip and load force rates did notscale to actual (or perceived) mass of

DiscussionThe SWI was induced in a single, unchanging cube when vision was occluded during lift. This cube felt

ReferencesFlanagan JR, Beltzner MA (2000) Independence of perceptual and sensorimotor predictions in the size–weight

illusion. Nat Neurosci 3:737–741.

Ch i A (1891) A l é i l d l élé d l i d id A hi d

actual (and identical) mass ofthe cubes.

scale to actual (or perceived) mass ofthe cubes.

heavy after seeing a small cube and light after seeing a big cube.

Expectations of heaviness are not only powerful enough to alter the perception of a single object’sweight, but also continually drive the forceswe use to lift the object when vision is unavailable.

Vision is required for the detection / correction of initial force errors, even though these errors areostensibly haptic. Can vision substitute for impaired somatosensation in clinical populations?

Charpentier A (1891). Analyse expérimentale: de quelques éléments de la sensation de poids. Archives de Physiologie Normale et Pathologique 3:122‐135.

AcknowledgementsThis project was funded with a postdoctoral fellowship awarded by DFAIT Canada to G. Buckingham. The authors would like to thankJim Ladich for constructing the size‐weight cubes, and Haitao Yang for technical support.