Thursday, October 16, 2014

Why are we fooled by the ventriloquist?

As we watch the movement's of a dummy's mouth while it is sitting in a ventriloguist's lap, we perceive the speech as coming from the dummy's mouth, rather than it's master's voice. Berger and Ehrsson show that this illusory translocation is associated with increased activity the left superior temporal sulcus (L. STS). This is the region that has been shown to be central in determining the spatial coordinates of our experienced self. (It is associated also, for example, with the out of body illusion.)
It is well understood that the brain integrates information that is provided to our different senses to generate a coherent multisensory percept of the world around us, but how does the brain handle concurrent sensory information from our mind and the external world? Recent behavioral experiments have found that mental imagery—the internal representation of sensory stimuli in one's mind—can also lead to integrated multisensory perception; however, the neural mechanisms of this process have not yet been explored. Here, using functional magnetic resonance imaging and an adapted version of a well known multisensory illusion (i.e., the ventriloquist illusion), we investigated the neural basis of mental imagery-induced multisensory perception in humans. We found that simultaneous visual mental imagery and auditory stimulation led to an illusory translocation of auditory stimuli and was associated with increased activity in the left superior temporal sulcus (L. STS), a key site for the integration of real audiovisual stimuli. This imagery-induced ventriloquist illusion was also associated with increased effective connectivity between the L. STS and the auditory cortex. These findings suggest an important role of the temporal association cortex in integrating imagined visual stimuli with real auditory stimuli, and further suggest that connectivity between the STS and auditory cortex plays a modulatory role in spatially localizing auditory stimuli in the presence of imagined visual stimuli.

1 comment:

  1. Thanks Champ, that was a good lead. I sent a letter to the Journal, but who knows if they will publish. Here is the text in case you're interested

    Dear Sirs

    My interest is as the author of a free book on skydrive at I provide an entirely original and simple approach to neuroscience. I value functional sites - every site of anatomy with effectors or receptors. I suggest a brain automatically and rapidly finalizes inputs and resolves outputs for manual functions at manual rates of function and thought. Although vast and rapid across networks, we experience "life" at manual rates of function because functions determine, and a brain serves functions as best it can.

    In your paper you go only as far as to say :

    "Together, these results suggest that the fusion of imagery and real sensory signals is mediated by the same integrative mechanisms in the association cortex and primary sensory cortex as those that mediate the fusion of real sensory stimuli."

    You can be bolder and say that the "fusion" for imagination serves the same inputs and outputs that apply to real vision. In fact, when seeing, we are always imagining along with the reality. It is an artificial distinction, because functional sites "think" by using neurons finalizing in a brain to integrate all diverse anatomical functions. The difference between loose visual imagination and sharp perception of vision by an eye is literally looseness or sharpness in function and processing. When loose, other functions tighten to take precedence to make up for having no real visual perception when imagining with eyes closed for example.

    Memory of past vision can be instigated and reworked, as imagination will always be a construct from past experiences in more and less novel ways. That instigation will involve the eye itself, but less that if the eye were seeing, and boosted by other functions working along with it and perhaps instigating more. Test conditions add to the instigation possibilities for subjects poised to perform in some way. All of this remains hidden because we need to look at the whole anatomy.

    If you get a chance to read my work, you can see how to break away from the brain to get a context for mind. Our functions are structured for awareness of space, time, cause, and effect - not merely "spatiality" (often ignoring time completely by saying it is an analogy of space in awareness). Even "cause" and "effect" are enshrined in functions identified in my book to the same extent as "space" is enshrined in eye function. "Time" is enshrined in ear function - sequential, non spatial. The structure is very straightforward. I hope this helps you make progress.

    Marcus Morgan