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Attentive tracking of multiple objects by humans and monkeys

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Summary

Can Monkeys Mentally Track Multiple Stimuli?

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Monkey M

%Correct

Items Tracked

Monkey B

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Human (N=5)

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ChanceChance

1) Monkeys can track 2 and humans can track 3-4 items.2) Humans discriminate form changes better on targets.3) In V4 tracked stimuli elicit higher firing rates.4) This response increase is not measurably diminished when a second stimulus is tracked.

Jude F. Mitchell, Kristy A. Sundberg & John H. Reynolds

18 of 29 neurons show significantly higher firing for targets in either 1 of 4 or in 2 of 4 tracking tasks.

* Monkeys made saccades to all targets and to no distracters to receive reward.

* Trajectories were identical to the monkey task. * Rings were replaced with figure 8’s.* At the motion pause, all items changed from 8’s to E’s or 3’s, except one that changed to either a 2 or 5. * Subjects tracked the targets and also reported by key-press whether a 2 or 5 was present.

Attention Task:

V4 responses are enhanced for tracked items. The strength of modulation issimilar for tracking 1 or 2 targets.

References1. Pylyshyn ZW and Storm RW (1988) Tracking multiple independent targets: evidence for a parallel tracking mechanism. Spat Vis. 3(3):179-97.2. Sears CR and Pylyshyn ZW (2000) Multiple object tracking and attentional processing. Can J Exp Psychol. 54(1):1-14.

* Systems Neurobiology Laboratory, The Salk Institute for Biological Studies. Funding provided by NIH Training Grant in Cognitive Neuroscience (J.M.), NSF Graduate Research Fellowship (K.S.), and NEI grant 1R01EY13802 (J.R.).

Task: while maintaining fixation, track all cued stimuli.

4-8 identcal stimuli appear

(200ms)

1-4 targets cued by luminance increment

(200ms)

Stimuli move to pause position

(750 ms)

Stimuli pause(300ms)

Stimuli move tofinal position

(750 ms)Cue off(200ms)

Fixation point disappears: saccade

To ALL targets and NO distracters to earn reward

Yes.Monkeys can track at least 2 stimuli

Are tracked stimuli attended?

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Human (N=5)

Target

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1 of 4 2 of 4 1 of 5 2 of 5 1 of 6 2 of 6 3 of 6

Items Tracked

1 of 4 2 of 4 1 of 5 2 of 5 1 of 6 2 of 6 3 of 6

Items Tracked

Distracter

Yes.Discriminationis betterfor trackedstimuli.

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Are V4 Neurons Modulated?

* The monkey attentively tracked targets far from the receptive field while oriented, colored gabors appeared throughout the visual field. The neuron’s spatial receptive field,color, and orientation tuning were computed on the basis of responses to the gabors..

Step 1) Mapping a V4 Unit’s Receptive Field

4 identical stimuli appear

(200ms)

1 targets cued by luminance increment

(100ms)


(750 ms)




Fixation point off: saccade to

the target

Tracking Away from RF

Flashing Gabors+

RF

RFRF

RF

RFRF

RFRF

RFRF

RF

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RFRF


(200ms)

1 targets cued by luminance increment

(100ms)


(750 ms)




Fixation point off: saccade to

the target

Tracking Away from RF

Flashing Gabors+

RFRF

RFRFRFRF

RFRF

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RFRFRFRF

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24681012

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Response to Flashed Gabor Image In x,y Space broken down by Orientation

# of Repeats per x,y position

0-33 ms

33-67 ms

67-100 ms

100-133 ms

133-167 ms

167-200 ms

ResponseWindow

TIME

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Fixation

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Fixation

Example Neuron:

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# of Repeats per x,y position

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33-67 ms

67-100 ms

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133-167 ms

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Response to Flashed Gabor Image In x,y Space broken down by Color

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Joint Color/Orientation Tuning for Example Cell:

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167-200 ms

Response Window

TIME

SpatialResponse

Orientation& Color

Response

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# of Repeats

Orientation

Color

X – stat. sig.> baseline

O – stat. sig.< baseline


(200ms)

1 or 2 targets cued by luminance increment

(100ms)


(750 ms)

Stimuli Pause(1000 ms)



Fixation point off: saccadeto ALL targets

RFRF

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Performance overRecording Sessions

1 of 4Tracking

2 of 4Tracking

Step 2) Preferred Stimuli Enter and Pause in the Unit’s Receptive Field During Tracking

We recorded 29 cells from Monkey M:

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Time (ms)

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Mean Response (N=29, All Cells)

Pause Resume

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Modulation = 21.4%

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Modulation = 29.0%

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AI Index1 of 4 Tracking

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Relative Attentional Modulation for 1 or 2 Target Tracking

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AI =Attended - Distracter

Attended + Distracter

Corr. = 0.76

NeuronShown Above

* Stat. Sig.

o Non-Sig.

* Stat. Sig.

o Non-Sig.

There were no significant differencesin the strength of modulation for thetracking of a single or two stimuli.

Pause Period

Stimuli pause(75 ms)

Stimuli pause(75 ms)Form Change

(150 ms)

Example Cell:

Unit C20.1: 1 of 4 Tracking

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Target Distracter

Unit C20.1: 2 of 4 Tracking

Gabor duration 33 msec., One gabor appeared every 8 msec., Resulting in 4 gabors being present at any point in time.

ResponseWindow

Target Distracter

Target Distracter