Understanding Velmans: The Third Hand

In the supernumerary hand illusion , a rubber hand placed alongside our real hand can get perceived as being part of our own body, giving us a third hand. This is a slight modification of the rubber hand illusion, where the actual hand is screened and the rubber hand is perceived as replacing the actual hand. See below.

Presumably, in Velman’s ‘reflexive monism’ terms, the rubber hand illusion would be explained as having the visual sensation of the rubber hand and the tactile sensation of the actual hand both being reflected back to the rubber hand. And in the supernumerary hand illusion, tactile sensation from the real hand is reflected back to both real and rubber hands. In both cases, visual information overrides tactile and prioperceptive senses. And both examples undermine the idea that consciousness arises from something outside of our heads.

A similar case is the well-known McGurk effect where visual overrides auditory input. For a good example, fast-forward below to time 1:24.

I haven’t found a video example for the double-flash illusion where auditory input overrides the visual. Wikipedia has a reference to a paper which suggests that timing of multimodal activation is too fast to be mediated by a higher order integration suggesting feed forward or lateral connections. In the rubber hand examples, inter-modal reflexive processes provide immediate sensation that is subsequently quoshed by higher-order functions . But with the McGurk effect, the initial impression with visual overriding auditory cannot be quoshed by higher-order functions – we still hear what we see even though we know it is wrong.

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2 Responses to Understanding Velmans: The Third Hand

  1. headbirths says:

    From Ramachandran’s ‘The Emerging Mind’ (pages 16-17): Some amputees have phantom limbs that feel paralysed. Speculation: this is ‘learned paralysis’: any attempt to move the phantom limb is met with visual feedback – ‘it won’t move’. Experimentation: prop up a mirror in front of the amputee such that when they look at their amputated arm they see a reflection of their other (intact) arm instead. Then, the amputee must try to make symmetrical movements to both arms. Now the brain gets the visual feedback from the phantom limb. Significantly: this relieves the pain of the phantom limb! Possibility: This technique might also be used to help stroke victims recover functions (note 6, page 137).

  2. Pingback: Empathy | Headbirths

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