Fragmented saccades inappropriate operation of the fixation system
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Fragmented Saccades: Inappropriate Operation of the Fixation System?. Edward Keller 1 and Kyoung-Min Lee 1,2 1 Smith-Kettlewell Eye Research Institute San Francisco 2 Seoul National University, Korea. Saccades are normally stereotyped, relatively straight, single movements

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Fragmented Saccades: Inappropriate Operation of the Fixation System?

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Fragmented saccades inappropriate operation of the fixation system

Fragmented Saccades: Inappropriate

Operation of the Fixation System?

Edward Keller1 and Kyoung-Min Lee1,2

1Smith-Kettlewell Eye Research Institute

San Francisco

2Seoul National University, Korea


Fragmented saccades inappropriate operation of the fixation system

Saccades are normally stereotyped, relatively straight, single movements

that end on a new target of interest.

They are intermixed with longer periods of stable fixation

Thus, normal operation of the saccadic system involves the seamless

alternation of movement and fixation, but under some circumstances this

carefully orchestrated interplay is interrrupted.


Fragmented saccades inappropriate operation of the fixation system

  • We have recently found two different situations in which

  • saccades become fragmented:

  • Late-onset Tay-Sachs disease (LOTS)

  • Tasks that involve saccades generated in response to difficult decision processes among multiple choices of response


Fragmented saccades inappropriate operation of the fixation system

Lots patient

(Rucker et al., 2004)


Fragmented saccades inappropriate operation of the fixation system

LOTS patient

Monkey stim. OPNs


Fragmented saccades inappropriate operation of the fixation system

Signals in the

brainstem immediate

Pre-motor network


Fragmented saccades inappropriate operation of the fixation system

Fragmented movements when saccades are generated

in a task which requires extensive cognitive processing


Fragmented saccades inappropriate operation of the fixation system

Typical choice response task

Reaction times in choice response tasks follow Hick’s Law, RT = T*log2(NA)


Fragmented saccades inappropriate operation of the fixation system

Targets

8NA

2NA

Masks

Cue

Saccade

Saccade

Time

Saccadic choice response task


Fragmented saccades inappropriate operation of the fixation system

900

90 %

800

700

600

choice response time (ms)

500

400

10 %

300

200

1

2

4

8

Number of alternatives

A

50

number of alternatives

1

2

4

8

40

30

# trials in 50-msec bin

20

10

0

100

300

500

700

900

1100

Choice response time (ms)


Fragmented saccades inappropriate operation of the fixation system

Fragmented two-step saccade

Normal single-step saccade

5

5

HEP

0

5

0

5

-5

-5

VEP (deg)

5

VEP (deg)

0

0

5

VEP

0

0

-5

-5

-5

0

5

-5

-5

0

5

-5

Time (ms)

HEP (deg)

HEP (deg)

Time (ms)


Fragmented saccades inappropriate operation of the fixation system

SCFN

n=43

Number of neurons

Time w/r to saccade end

(Everling et al. 1998)


Fragmented saccades inappropriate operation of the fixation system

Signals in the

brainstem immediate

Pre-motor network


Fragmented saccades inappropriate operation of the fixation system

SCFN


Fragmented saccades inappropriate operation of the fixation system

FEF Sommer et al.


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