SFN99 poster

1
Dissociation of Planning and Execution Stages in
Voluntary Movements of Visual Spatial
Attention Chad J. Hazlett, Marty G.
Woldorff Center for Cognitive Neuroscience, Duke
University, Durham, NC, 27708
Figure 2 Distance effect (far-minus-near RT)
under multiple conditions.
Introduction
Fig. 2.1
Fig. 2.2
Fig. 2.3
Fig. 2.4
Fig. 2.5

• The literature is unresolved as to whether the
  time it takes to shift visual spatial attention
  is distance-dependent (Egly Homa, 1991 Tsal,
  1983 Shulman, Remington, McLean, 1979), or
  distance-independent (Sperling Weichselgartner
  1995 Kwak, Dagenbach, Egeth, 1991).
• Some studies have had confounds between
  shift-distance and retinal eccentricity (e.g.
  Shulman et al, 1979, Sperling Weichselgartner,
  1995).
• In addition, in some studies subjects knew in
  advance where they would shift attention, and in
  others they did not.
• We used a novel double-cueing technique to study
  the spatio-temporal properties of shifts in
  covert visual attention without eccentricity
  confounds.

Distance Effect (Far-Near RTs)
Exp. 1A Attention shifts with planning and
execution
Exp. 1C EOG calibration (full eye movements)
Exp. 1B Control for retinal position
Exp. 2A Attention shifts with execution only
Exp. 2B Control for retinal position.
plt.001
Experiment 1 Distance Effect With
PlanningExecution

• Experiment 1B (Control for Retinal Position)
• Rationale
• Although equally eccentric in Exp. 1A, the
  retinal positions of near and far targets were
  still different. Exp. 1B was designed to
  empirically verify that results in Exp1 were due
  to attentional-movement path-length difference
  and not target position per se.
• Design
• Same setup and subjects as 1A, but subjects were
  cued from the center box to shift attention
  directly to one of the bottom or lateral boxes
  for A/H discrimination.
• Analysis
• Same as main experiment (1A).
• Results
• Target position alone did not affect RT
  (far-minus-near -19ms, t-1.6, p.147) (fig.
  2.2).
• Experiment 1C (EOG Calibration for Experiment)
• Rationale
• To determine EOG magnitude for eye movements of
  known size.
• To determine how intentional eye movements alter
  distance effect in 1A.

• Experiment 2B (Control for Retinal Position)
• Rationale
• Same as Exp. 1B to verify that target position
  alone did not impact on RTs.
• Design
• Cue from center position instructs subjects to
  shift attention to bottom/lateral boxes, where
  they make button press based on go/no-go
  discrimination.
• Analysis
• Same as Exp. 1B.
• Results
• Target position alone had no effect on RTs (mean
  difference15ms, t1.5, p.80). See fig. 2.5.

Lateral Boxes

Experiment 2 Dissociation of planning and
execution

• General Conclusions
• Covert shifts in visual spatial attention
  consist of two phases execution and planning.
• The duration of of the planning stage is
  distance dependent while the duration of the
  execution stage is distance-invariant (fig. 4).

• Experiment 1A (Main)
• Design
• 11 subjects (5 male, 6 female, age 18-40,
  right-handed).
• 7 boxes always on screen 1 at fixation, other 6
  at equal eccentricities (fig 1).
• First cue at fixation instructs subjects to
  covertly shift attention to one of the upper
  boxes. Second cue at cued upper box position
  instructs subjects to covertly shift attention to
  bottom (far) or lateral (near) box on same side.
  (fig 1)
• At final position subjects make an A/H
  discrimination (button response).
• Eye movements minimized by practice, monitored
  by camera, and recorded with EOG (vertical and
  horizontal electrodes on left and right).
• Analysis
• RT data rejected per trial for any of following
  reasons
• (1) incorrect response,
• (2) occurred with large eye movement or blink
  (gt110uV), or
• (3) RT came more than 2 standard deviations away
  from mean (per subject).
• T-tests to compare RTs for near and far
  trials.
• Results
• Far trials required 70ms longer than near
  trials (t5.1 , p.0004).(fig 2.1).
• Little eye movement observed (lt.85 degrees see
  blue trace on fig 3).

• Experiment 2A (Main)
• Rationale
• Distance effect in Exp. 1A may have occurred in
  planning or execution stage.
• Experiment 2A differs from Exp 1A only in that
  subjects can pre-plan shifts in attention.
  Thus RTs in experiment 2A measure only the
  effects of execution and not planning.
• Design
• 12 subjects (8 female, 4 male, age 18-40,
  right-handed).
• Same stimulus layout as Exp 1A.
• First cue (from the center position) cued
  attention to one of the four lateral/bottom
  boxes.
• At cued location, difficult go/no-go
  discrimination instructed subjects when/if they
  should move attention up to top box on attended
  side. At the top box thus cued, subjects
  performed A/H discrimination as in Exp 1A.
• Allows subjects to pre-plan attentional movements
  separately from execution (ie, before move-cue).
• Analysis
• Same as Exp 1A.
• Results
• Now, with pre-planning possible, shift distance
  did not affect RTs. (far-minus-near6ms, t.49,
  p.93). See fig. 2.4.

PrCG
MFG
References   Tsal, Y. 1983. Movements of
Attention Across the Visual Field. J. of Exp.
Psychology, 17 551-560.   Kwak H, Dagenbach D,
Egeth H. 1991 Further evidence for a
time-independent shift of the focus of
attention. Perception Psychophysics.
5473-480.   Schulman G, Remington R, McLean J.
1979. Moving attention through visual space. J.
Exp. Psychology. 5522-526.   Sperling G,
Weichselgartner E. 1995. Episodic theory of the
dynamics of spatial attention. Psychological
Review. 102503-532. Egly R, Homa, D. 1991.
Reallocation of visual attention. Human
Perception Performance. 17(1)142-59.

• Conclusions from Experiments 1A-1C
• Time required to voluntarily shift covert visual
  spatial attention is distance-dependent. (fig
  2.1)
• This effect is due to path-length differences
  for attentional-movements rather than target
  position or eye movements.

Supported by NIMH-ROI-MH60415 to M.G.W.