Dear Keith and dear all, eye movements smoothly pursuing non-visual targets have been studied and documented in particular in the '70 and '80 of last century. Dr. de' Sperati already provided a number of references. You may also consider Gauthier & Hofferer (1976) and Buizza et al. (1979), about the possibility of pursuing moving sounds provided the acoustic information is complemented by additional, congruent motion information (e.g. proprioceptive or vestibular), and Van der Steen et al. (1983) about the possibility of pursuing illusory motion created by strobe lighting.
Young and Yasui (1975) suggested that SP movements can be produced if the available sensory information (regardless of its origin) is enough to allow the CNS to reconstruct an internal target velocity signal (perceptual feedback hypothesis, see also Young 1977), but of course this doesn't include the case of imagined targets.
Personally, I remember an adult subject (male, 30-35 ys old) able to produce eye movements that looked very similar to SP movements, and lasting a few seconds, when pursuing self-imagined targets or the harmonic motion of a sound. He was the only one to do so in a sample of more than 15 sbjs, and we didn't further explore this behaviour.
I don't know whether anybody systematically studied those phenomena or statistics are available about the percentage of subjects able to perform such movements. And I don't know whether anybody was able to prove that the features of such movements are the same as those of the visually evoked pursuit movements, or they actually are a different kind of eye movement.
Sincerely
Angelo Buizza
Dept. Computers and Systems
University of Pavia
via Ferrata 1
I-27100 Pavia - Italy
tel. +390382985359, fax +390382985373
----- Original Message -----
From: Claudio de'Sperati
To: [log in to unmask]
Sent: Friday, March 14, 2008 9:58 AM
Subject: Re: [EM_LIST] smooth pursuit without a target
Dear Keith, making smooth pursuit eye movements without a target indeed is
not impossible, as instead often claimed, although not too common. I don't
know how freqeutnly this occurs in children, but in adults there are studies
clearly showing this phenomenon under certain circumstannces.For example, we
can pursue the reconstructed representation of a stimulus (the "percept")
rather than the retinal stimulus (e.g., Steinbach 1976). Also, after
stimulus offset pursuit continues for a short while (e.g., Whittaker &
Eaholtz 1982), and anticipatory smooth eye movements can be volitionally
controlled (e.g., Barnes et al 1997). We documented sustained (up to about
20 seconds) smooth pursuit eye movements during mental extrapolation of
motion (de'Sperati and Santandrea 2005). Arousal/attention level seems to be
a relevant factor, and perhaps children have a different relationship
between arousal/attention, saccades and smooth pursuit.
All the best
_______________________________________________
Claudio de'Sperati, PhD
Associate Professor, Università Vita-Salute San Raffaele
Via Olgettina 58, 20132 Milano, Italy
Phone no. +39 02 2643 4859, Fax no. +39 02 2643 4892
Home page: http://www.unisr.it/docenti/ricerca/desperati/
_______________________________________________
----- Original Message -----
From: "Ramesh Mishra" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 14, 2008 5:21 AM
Subject: Re: [EM_LIST] smooth pursuit without a target
> A very good observation indeed. I too have seen so sometimes.
> Ramesh Mishra
>
>
> On 3/14/08, Keith_Karn <[log in to unmask]> wrote:
> > Dear Eye-movement list members -
> > The other day I was watching my 5 year old daughter learn to roll her
> > eyes. I was surprised by what I saw - not that a 5 year old rolling her
> > eyes isn't surprise enough. ;-) It appeared that she was marking
> > smooth (pursuit-like) eye movements without a target. I've just
> > observed a few others trying a similar movement (moving the eyes back
> > and forth while close to their maximum deviation in the orbit). It
> > appears that others can make similar movements. Has this type of eye
> > movement been previously documented?
> >
> > Keith Karn
> > [log in to unmask]
> >
> > --
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>
>
> --
> Ramesh Kumar Mishra PhD
> Centre for Behavioural and Cognitive Science
> University of Allahabad
> Allahabad 211002
> India
> Email:[log in to unmask]
> Ph-91-0532-2460738 ( work)
> Mob-91-9451872007
> Fax-91-0532-2460738( work)
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> Home page: www.cbcs.ac.in
>
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