I think they are corrective saccades. On 9 out of the 40 saccades your
present, I think the subject lands within ~2 deg (from 0.5 to 3 deg) of
the target, and then, after a ~100-150 ms pause, makes a corrective
saccade. The obligatory intersaccadic interval is a bit shorter for
a corrective saccade than for, say, a standard visually-guided saccade.
I'd still expect more like a 200 ms pause between the initial and
corrective saccade, but 100-150 is not too surprising.
If you are sampling fast enough than you might be able to see that there
are two distinct saccades, each sitting on the main sequence at a location
appropriate for its amplitude.
By the way, what are you doing about blinks? You show 40 seconds of data.
There must be a fair number of blinks occurring in that time. I notice
two instances where the eye trace disappears, starting with the beginning
of the saccade and ending about a degree from the end of the saccade.
I'm guessing those are blinks. But your subject made more than 2 blinks
in 40 seconds, unless they are very unusual. That's really worth knowing
more about - your software may be "handling" those other blinks for you,
and in the process distorting your traces (e.g., replacing some blink
periods with linear interpolation).
larry
On Fri, 3 Sep 2010, Komogortsev, Oleg V
wrote:
> Thank you everyone for responding, your ideas and references. Just to
> clarify the sampling rate of the recording was 1000Hz, therefore each
> sample is equivalent to 1ms. To provide a more general picture of what
> is happening my student has uploaded another image
> http://daizanxun.blog.com/files/2010/09/eye-movement-zoomed-out.jpg
> where overall view is available - blue line represents the stimulus
> position (jumping dot), green signal is recorded eye position trace,
> black circle identifies the event which is enlarged in the previous
> image. Only horizontal component of the signal is presented, I will try
> to get an enlarged image of the vertical component of movement and
> provide the link.
>
> Detailed Task Description: The stimulus was presented as a 'jumping
> point' with vertical coordinates fixed to the middle of the screen. The
> first point was presented at the middle of the screen while subsequent
> points moved horizontally to the left and right of the screen's center
> with a special amplitude of 20 deg. The jumping sequence consisted of
> 100 points including the original center point, yielding 14 stimulus
> saccades for each test trial. After each jump, the point remained
> stationary for 1s before the next jump was initiated. The size of the
> point was approximately 1deg of the visual angle with the center marked
> as a black dot. Each point consisted of white pixels (except for the
> central black dot) on a black screen background.
>
>
> ---Oleg
>
> ---
> Dr. Oleg Komogortsev
> Assistant Professor
> Texas State University-San Marcos
> Department of Computer Science
> 601 University Drive
> San Marcos, TX 78666-4616
> Phone: (512) 245-0349 Fax: (512) 245-8750
> Email: [log in to unmask]
> Webpage: www.cs.txstate.edu/~ok11
>
>
> -----Original Message-----
> From: Eye-movement mailing list [mailto:[log in to unmask]] On Behalf Of Andreas Sprenger
> Sent: Friday, September 03, 2010 12:38 PM
> To: [log in to unmask]
> Subject: [EM_LIST] AW: Automated recognition of complex oculomotor behaviour
>
> Hi,
>
> I think you recorded a multistep saccade as reported by Rucker et al (2004) or Huebner et al (2007). You will find detailed information in Leigh & Zee: The Neurology of Eye Movements, Chapter 3. These multistep saccades can be found in patients as well in healthy controls (but to a lesser proportion ;-)).
>
> Cheers
>
> Andreas
>
>
>
> Rucker JC, Shapiro BE, Han YH, et al. Neuroophthalmology of late-onset Tay-Sachs disease (LOTS). Neurology 2004;63:1918-1926.
> Huebner J, Sprenger A, Klein C, et al. (2007). Eye movement abnormalities in spinocerebellar ataxia type 17 (SCA17). Neurology. Sep 11; 69(11):1160-8.
>
>> -----Ursprüngliche Nachricht-----
>> Von: Eye-movement mailing list
>> [mailto:[log in to unmask]] Im Auftrag von Komogortsev, Oleg
>> V
>> Gesendet: Freitag, 3. September 2010 17:24
>> An: [log in to unmask]
>> Betreff: [EM_LIST] Automated recognition of complex oculomotor
>> behaviour
>>
>> Hello everybody,
>>
>> In our lab we are trying to develop reliable algorithms for
>> classification of complex oculomotor behavior, with some details
>> described in http://ecommons.txstate.edu/cscitrep/18/
>> Recently we have acquired EyeLink II and we are trying to classify
>> some of the oculomotor events that became visible when recording is
>> conducted at the frequency of 1000Hz or higher.
>> We are presenting horizontal step stimulus to the subject.
>>
>>
>> We have encountered an event where a saccade to a target is slightly
>> broken in the middle, the event does not look like an express saccade,
>> i.e. there is not enough latency in the between the pieces. The
>> picture of the event is present here
>> http://daizanxun.blog.com/files/2010/09/eye-movement.jpg
>>
>>
>> My question what is it?
>>
>> May be it is equipment slippage? Or maybe saccade trajectory change
>> during some sort of the neuronal control noise during saccade's pulse?
>> I was not been able to find an example of this type of behavior in the
>> research literature and I was hoping that somebody would be able to
>> point me to the correct source.
>>
>> Thank you in advance.
>>
>> ---Oleg
>>
>> ---
>> Dr. Oleg Komogortsev
>> Assistant Professor
>> Texas State University-San Marcos
>> Department of Computer Science
>> 601 University Drive
>> San Marcos, TX 78666-4616
>> Phone: (512) 245-0349 Fax: (512) 245-8750
>> Email: [log in to unmask]<mailto:[log in to unmask]>
>> Webpage: www.cs.txstate.edu/~ok11<http://www.cs.txstate.edu/~ok11>
>>
>>
>> --
>> EYE-MOVEMENT mailing list ([log in to unmask]) N.B.
>> Replies are sent to the list, not the sender To unsubscribe, etc. see
>> http://www.jiscmail.ac.uk/files/eye-movement/introduction.html
>> Other queries to list owner at [log in to unmask]
>>
> --
> EYE-MOVEMENT mailing list ([log in to unmask])
> N.B. Replies are sent to the list, not the sender
> To unsubscribe, etc. see http://www.jiscmail.ac.uk/files/eye-movement/introduction.html
> Other queries to list owner at [log in to unmask]
>
> --
> EYE-MOVEMENT mailing list ([log in to unmask])
> N.B. Replies are sent to the list, not the sender
> To unsubscribe, etc. see http://www.jiscmail.ac.uk/files/eye-movement/introduction.html
> Other queries to list owner at [log in to unmask]
>
--
Larry Snyder [log in to unmask]
Associate Professor of Neurobiology www.eye-hand.wustl.edu
Washington University, School of Medicine Office: (314) 747-3530
Dept of Anatomy & Neurobiology, Box 8108 Lab: (314) 747-4095
660 S Euclid Ave, St. Louis, MO 63110 Fax: (314) 747-4370
--
EYE-MOVEMENT mailing list ([log in to unmask])
N.B. Replies are sent to the list, not the sender
To unsubscribe, etc. see http://www.jiscmail.ac.uk/files/eye-movement/introduction.html
Other queries to list owner at [log in to unmask]
|