innthe example given a figure of 30 degrees per second is fair because the
eye is inherently pre disposed not to track in smooth pursuit ANY thing
which is repetitive. you are constantly fighting when working with the eye
the complex interaction of perception with the basic opto elctro mechanics
of the eye. the limits of the "mechanics" are way above what is generally
required but the perception loop plays truly terrifying tricks in terms of
what it reports to the brain that you see and what the eye actually looks
at.
Secondly if you are using a screen it will have to an alolgue type scope or
similar it is futile to investigate smooth pursute on a 30 or 60 fps screen
and even a 120fps is bad if you are looking for precision.
To give an idea of the range of the problem a typical person "off the
street" will maintain pursuit in an arrangment such as you describe to
around 30 to 35 degrees per second. conversely after only a little training
this can be raised to 400 degrees per second!
stereo pursuit will maintain up to smilar speeds but stereo pursuit breaks
quickly as the resolution falls in failure to maintain fovial alingment. at
this point the eye balistically saccades to the expected terminus or in the
case of a repetitie stimulus it will sacade to the start.
Scott.
----- Original Message -----
From: "Rogers" <[log in to unmask]>
To: <[log in to unmask]>
Sent: 09 November 2000 12:12
Subject: Re: smooth pursuit velocity thresholds
> Hi Scott
>
> Thanks for your reply. I can see that the issue is more complex
> than I originally thought. I never considered target aquasition as
> part of the process because this is not really what I'm trying to get
> at. To be more precise, if say, in an experiment where participants
> were asked to look at a screen which had a continuous series of
> dots moving across it in a straight line (left to right for arguemnt
> sake) x distance apart. When the dots where moving slowly I
> would expect the velocity (speed and direction) of persuit
> eyemovements to be equivalent to the velocity of any given dot
> and a large sample of data over time to take on a typical saw tooth
> pattern as the observer follows one dot for a while and then jumps
> back to a new dot etc. What I'd like to know is, at what speed (if
> any) will the perceptual system abandon this continuous pattern of
> eye movement (we might refer to this as multiple fixations over
> time in a repetative smooth persuit task)? Consider this
> naturalistic example. If looking from a window of a moving train at
> a series of poles set in the ground x distance apart and y distance
> from the railway line. What speed will the train be moving when the
> perceptual system naturally gives up on fixating and tracking
> particular poles?
>
> Best Regards
>
> Steve
> > hi
> > The "handbook of perception and human performance" Vol 1 (New York
Wiley)
> >
> > is probably the best resource for this type of data.
> >
> > of course there is a limit but it is very high for all practical
purposes.
> > The main problem is aquiring a pursuit of a fast target. It is very hard
to
> > aquire a target because the feedback is so slow. most lauch mechanisms
for
> > fast targets are ambiguous (note there is NO point in trying to simulate
> > this on video!!!) it is possible to track tracer amunition at side view
> > standing only a few feet away from a supersonic rifle because the tracer
> > ingites some small distance from the barrel at a point nearly coincident
> > with the sonic boom and so produces a very easily aquired target.
whereas a
> > much slower object such as a ball from a pitcher is initially hard for
a
> > subject to track as the eye tends to continue pursuit of the pitshers
hand
> > before attempting to re aquire the ball. If the subject is untrained the
> > requirement for conscious intervantion mens a delay of around 300 mS
before
> > the target can be re aquired by which time it is nearly in the catchers
mit.
> > With some small training however the track is very much improved.
> >
> > Scott
> > ----- Original Message -----
> > From: "Rogers" <[log in to unmask]>
> > To: <[log in to unmask]>
> > Sent: 08 November 2000 14:32
> > Subject: smooth pursuit velocity thresholds
> >
> >
> > > Dear members
> > >
> > > Can anybody direct me to research/papers that has tested for the
> > > maximum velocity that the eye can track a moving target (i.e. is
> > > there a velocity threshold where smooth persuit movements fail to
> > > keep up with a moving target?).
> > >
> > > Many thanks and best regards
> > >
> > > Steve Rogers
> > > Steve Rogers (BSc Hons, PGDip)
> > > Centre for Ecological Psychology
> > > Department of Psychology
> > > University of Portsmouth
> > > King Henry Building
> > > Portsmouth
> > > PO1 2DY
> > > Tel: (01705) 846322
> > > Fax: (01705) 846300
> > > email: [log in to unmask]
> > >
> >
>
>
> Steve Rogers (BSc Hons, PGDip)
> Centre for Ecological Psychology
> Department of Psychology
> University of Portsmouth
> King Henry Building
> Portsmouth
> PO1 2DY
> Tel: (01705) 846322
> Fax: (01705) 846300
> email: [log in to unmask]
>
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