Bilateral Attentional Advantage in Gabor Detection

1
Bilateral Attentional Advantage in Gabor Detection
Poster 63.405 Abstract 1095
Nestor Matthews Jenna Kelly
Department of Psychology, Denison University,
Granville OH 43023 USA
Introduction
Discussion
Method
In principle, visual performance could be
uniform within (unilateral) and across
(bilateral) the left and right hemifields.
However, previous research has revealed bilateral
advantages on relatively high level visual tasks,
such as letter identification (Awh Pashler,
2000 Chakravarthi Cavanagh, 2006), and motion
tracking (Alvarez Cavanaugh, 2005). Recently,
this bilateral advantage has been demonstrated
even on the elementary task of detecting Gabor
targets among Gabor distracters (Reardon, Kelly
Matthews, 2009). In the
present study, we investigated the extent to
which this bilateral superiority in detecting
Gabor targets among Gabor distracters is more
appropriately attributed to surround suppression
or to attention. These two make different
predictions, described in turn. Surround
suppression is the phenomenon in which
sensitivity to a target's luminance contrast is
reduced by a spatially displaced distracter
(Petrov, Popple McKee, 2007). In the present
detection study, surround suppression would be
evidenced by a distracter-induced decrease in hit
rates i.e., a decrease in yes responses on
target-present trials. Attention is the
selection of a sensory event. Attentional
selection can fail under conditions of temporal
crowding -a form of inappropriate
target-distracter integration that occurs when
stimuli are flashed briefly enough to overload
attentional selection (Pelli, Palomares Majaj,
2004). In the present detection study, a failure
of attention would be evidenced by a
distracter-induced increase in false alarm rates
i.e., an increase in yes responses on
target-absent trials. We further sought to alter
the difficulty of peripheral attentional
selection by varying the duration of a foveally
presented target letter.
Our primary finding is that the bilateral
superiority in Gabor detection reflects an
attentional limit, rather than surround
suppression. This was evidenced by the finding
that the main effect of laterality was
significant and large for false alarms (our proxy
for attentional selection), but non-significant
and small for hits (our proxy for surround
suppression). Indeed, bilateral and unilateral
hit rates were statistically indistinguishable
from each other across duration-by-distracter
pairings. Importantly, peripheral
stimulation remained identical across variations
in the foveal letters duration. Consequently,
the improvement with foveal letter duration
suggests that a neural resource shared by the
fovea and the periphery constrained performance.
Relative to the bilateral response, the
unilateral response at each letter duration
exhibited a failure to exclude distracters not a
failure to detect contrast. The pattern of
results implicates bilateral superiority in
attention, even on this most elementary visual
task. Even when the distracters were
absent, false alarms (but not hits) at the
briefest letter duration were significantly
higher unilaterally than bilaterally. The
difference in false alarm rates between
unilateral and bilateral conditions was inversely
related to foveal letter duration. One possible
explanation for this is that with decreasing
foveal letter duration, the noise mask was more
frequently misconstrued as the target itself a
failure of attentional selection.
Stimulus Sequence On Each Trial
Target/ Distracter Configurations
Experimental Details
Display Details

• Participants13 Denison University undergraduates
• IVs 2 (Laterality) x 2 (Distracter) x 3 (Letter
  Duration)
• Laterality Bilateral versus Unilateral
• Distracter Absent versus Present
• Letter Duration 67, 117, or 167 ms (8, 14, or 20
  screen refreshes)
• DVs
• Hits Yes response when Gabor target present
• False Alarms Yes response when Gabor target
  absent

• Foveal letter to (peripheral) Gabor target 14.55
  deg (center to center)
• Gabor target to nearest Gabor distractor 7.1 deg
  (center to center)
• Separation exceeded limit for spatial crowding
  i.e., 0.1 and 0.5 times the target eccentricity
  in the tangential and radial directions,
  respectively (Toet Levi, 1992).
• Two different configurations for each laterality
  condition
• Target-distracter offset Vertical or Horizontal
• Noise mask after each target and distracter 8 ms
  (1 screen refresh)
• Gabor target duration 183 ms (22 screen
  refreshes, regardless of letter duration)

Results





References
Alvarez Cavanagh (2005). Independent resources
for attentional tracking in the left and right
visual hemifields. Psychological Science 16(8),
637-643. Awh Pashler (2000). Evidence for split
attentional foci. Journal of Experimental
Psychology Human Perception and Performance
26(2), 834-846. Chakravarthi Cavanagh (2006).
Hemifield independence in visual crowding. Vision
Sciences Society, 274 (abstract). Petrov, Popple
McKee (2007). Crowding and surround
suppression Not to be confused. Journal of
Vision, 7(2), 1-19. Pelli, Palomares Majaj
(2004). Crowding is unlike ordinary masking
distinguishing feature integration from
detection. Journal of Vision, 4(12),
1136-1169. Reardon, Kelly Matthews (2009).
Bilateral Attentional Advantage on Elementary
Visual Tasks. Vision Research, 49(7),
692-702. Toet Levi (1992). The two-dimensional
shape of spatial interaction zones in the
parafovea. Vision Research, 32(7), 1349-1357.
Factor Hits
Laterality F(1,12)0.383, p0.547, pEta20.031, power0.088
Distractor F(1,12)11.222, p0.006, pEta20.483, power0.867
Letter Duration F(2,24)4.181, p0.028, pEta20.258, power0.679
Lat x Dist F(1,12)0.00, p1.00, pEta20.000, power0.05
Lat x Letter Dur F(2,24)0.331, p0.722, pEta20.027, power0.097
Dist x Letter Dur F(2,24)11.814, plt0.001, pEta20.496, power0.988
Lat x Dist x Letter Dur F(2,24)0.579, p0.568, pEta20.046, power0.135
Factor False Alarms
Laterality F(1,12)15.026, p0.002, pEta20.556, power0.944
Distractor F(1,12)14.204, p0.003, pEta20.542, power0.932
Letter Duration F(2,24)3.508, p0.046, pEta20.226, power0.598
Lat x Dist F(1,12)3.833, p0.074, pEta20.242, power0.437
Lat x Letter Dur F(2,24)2.305, p0.121, pEta20.161, power0.422
Dist x Letter Dur F(2,24)1.055, p0.364, pEta20.081, power0.213
Lat x Dist x Letter Dur F(2,24)0.458, p0.638, pEta20.037, power0.116


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