Saccadic eye movements cause compression of time as well as

space

Concetta Morrone, Ross & Burr

• Saacades allow area of high resolution to be pointed to to regions of interest in the visual scene

• It is of interest– What visual information is available during

saccades– How is what we were looking at and what we

are going to look at integrated

• Concetta Morrone, Ross & Burr and others have reported previously that – when a stimulus is flashed it is shifted in

perceived location in the direction of the saccade

– Space around the saccade target is compressed

• Suggested that this may be to do with the anticipatory shifts of LIP receptive fields

• LIP neurons have been found to encode temporal duration.

• Is there a compression of time around saccade onset

• Subjects fixated on a black spot (1deg)• On a warning (auditory??) fixation disappeared and a

target appeared 30 deg to the right.• Subjects saccaded to target with a mean of about 160

ms (this is not reported very accurately) • Bars shown sequentially with 100 ms SOA at random

times relative to saccade target onset for 8 ms each (TEST)

• Bars are shown sequentially at a variable SOA (between 8 and 200 ms) 2 seconds after TEST (PROBE)

• Verbal response - which was longer - 1st or 2nd

Expt 1

Fig 2a

• TEST shown 400 to 200 ms (mean of temporal interval) prior to saccade– shows PSE of ~100 ms and std dev of ~40 ms

• TEST shown 100 to 50 ms prior to saccade onset– Show PSE of ~50ms

• Control conditions of short vertical bars at saccade target, voluntary blinks and auditory clicks

Fig 2b

• Observed compression over a range of saccade sizes (3.5 – 45 deg) even though duration varied from 30 – 120 ms

• This seems to have come from nowhere and not mentioned in the methods. I really don’t know what they did here. I can guess but I don’t know

Fig 3

• Found PSE’s and stdevs at various time periods in which TEST was shown (overlap in trials)

• Showed PSE and Std dev becoming shorter

• Perceived duration of TEST decreases around the saccade onset. The perception becomes more definite

• Worried about the bimodal duration / precision plot?

Expt 2

• Temporal order of bars and estimate the size of the separation

• Method not really reported

• Assume same as Expt 1

Method ?

• Subjects fixated on a black spot (1deg)

• On a warning (auditory??) fixation disappeared and a target appeared 30 deg to the right.

• Subjects saccaded to target with a mean of about 160 ms (this is not reported very accurately)

• Bars shown sequentially with variable SOA at random times relative to saccade target onset for 8 ms each

• Verbal response - Temporal order of bars and estimate the size of the separation

Fig 4ab

• For judgements made on pairs shown 76 – 200 ms prior to saccade onset proportion correct is good with a small drop around saccade onset

• For judgements made on pairs shown less than 76 ms before saccade onset proportion correct decreased dramatically. In fact on bars are reported to be seen in the opposite order

Fig 4cd

• For judgements made on pairs shown 76 – 200 ms prior to saccade onset psychometric function is as would be expected

• For judgements made on pairs shown less than 76 ms before saccade onset psychometric function shows this mad triphasic pattern

Fig 4ef

• Estimates of stimulus separation is very good when pairs are shown 100 ms prior to saccade

• These estimates become multimodal around saccade as pairs are shown less than 76 ms prior to saccade onset

Explanations

• Attention

• Low level processing

• Chronostasis

• Shifting receptive fields and internal clocks