Saarela, T. P. & Landy, M. S. (2015).
Integration trumps selection in object recognition.
Current Biology, 25, 920-927.
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[Link to article]
[Press release]
[Covered at futurity.org]
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[BibTeX reference | .bib-file]
@Article{Saarela_Landy_2015,
author = {Saarela, T. P. and Landy, M. S.},
title = {Integration trumps selection in object recognition},
journal = {Current Biology},
year = {2015},
volume = {25},
number = {7},
pages = {920--927},
abstract = {Finding and recognizing objects is a fundamental task of
vision. Objects can be defined by several “cues”
(color, luminance, texture, etc.), and humans can
integrate sensory cues to improve detection and
recognition. Cortical mechanisms fuse information
from multiple cues, and shape-selective neural
mechanisms can display cue invariance by responding
to a given shape independent of the visual cue
defining it. Selective attention, in contrast,
improves recognition by isolating a subset of the
visual information. Humans can select single
features (red or vertical) within a perceptual
dimension (color or orientation), giving faster and
more accurate responses to items having the attended
feature. Attention elevates neural responses and
sharpens neural tuning to the attended feature, as
shown by studies in psychophysics and modeling,
imaging, and single-cell and neural population
recordings. Besides single features, attention can
select whole objects. Objects are among the
suggested “units” of attention because attention to
a single feature of an object causes the selection
of all of its features. Here, we pit integration
against attentional selection in object
recognition. We find, first, that humans can
integrate information near optimally from several
perceptual dimensions (color, texture, luminance) to
improve recognition. They cannot, however, isolate a
single dimension even when the other dimensions
provide task-irrelevant, potentially conflicting
information. For object recognition, it appears that
there is mandatory integration of information from
multiple dimensions of visual experience. The
advantage afforded by this integration, however,
comes at the expense of attentional selection.},
doi = {10.1016/j.cub.2015.01.068},
url = {http://www.sciencedirect.com/science/article/pii/S0960982215001323},
keywords = {}
}
Saarela, T. P. & Landy, M. S. (2012).
Combination of texture and color cues in visual
segmentation.
Vision Research, 58, 59-67.
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[Link to article]
[pdf]
[BibTeX reference | .bib-file]
@Article{Saarela_Landy_2012,
author = {Saarela, T. P. and Landy, M. S.},
title = {Combination of texture and color cues in visual segmentation},
journal = {Vision Research},
year = {2012},
volume = {58},
number = {},
pages = {59--67},
abstract = {The visual system can use various cues to segment the
visual scene into figure and background. We studied
how human observers combine two of these cues,
texture and color, in visual segmentation. In our
task, the observers identified the orientation of an
edge that was defined by a texture difference, a
color difference, or both (cue combination). In a
fourth condition, both texture and color information
were available, but the texture and color edges were
not spatially aligned (cue conflict). Performance
markedly improved when the edges were defined by two
cues, compared to the single-cue
conditions. Observers only benefited from the two
cues, however, when they were spatially aligned. A
simple signal-detection model that incorporates
interactions between texture and color processing
accounts for the performance in all conditions. In a
second experiment, we studied whether the observers
are able to ignore a task-irrelevant cue in the
segmentation task or whether it interferes with
performance. Observers identified the orientation of
an edge defined by one cue and were instructed to
ignore the other cue. Three types of trial were
intermixed: neutral trials, in which the second cue
was absent; congruent trials, in which the second
cue signaled the same edge as the target cue; and
conflict trials, in which the second cue signaled an
edge orthogonal to the target cue. Performance
improved when the second cue was congruent with the
target cue. Performance was impaired when the second
cue was in conflict with the target cue, indicating
that observers could not discount the second cue. We
conclude that texture and color are not processed
independently in visual segmentation.},
doi = {10.1016/j.visres.2012.01.019},
url = {http://www.sciencedirect.com/science/article/pii/S0042698912000399},
keywords = {Visual segmentation},
keywords = {Texture},
keywords = {Color},
keywords = {Cue combination},
keywords = {Signal detection theory}
}
Saarela, T. P., Westheimer, G., & Herzog,
M. H. (2010). The effect of spacing regularity on visual
crowding. Journal of Vision, 10(10):17, 1-7.
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[Link to
article]
[BibTeX reference | .bib-file]
@article{Saarela_etal_2010,
author = {Saarela, T. P. and Westheimer, G. and Herzog, M. H.},
title = {The effect of spacing regularity on visual crowding},
journal = {Journal of Vision},
year = {2010},
volume = {10},
pages = {1--7},
number = {10},
month = {8},
abstract ={Crowding limits peripheral visual discrimination and
recognition: a target easily identified in isolation
becomes impossible to recognize when surrounded by
other stimuli, often called flankers. Most accounts
of crowding predict less crowding when the
target-flanker distance increases. On the other
hand, the importance of perceptual organization and
target-flanker coherence in crowding has recently
received more attention. We investigated the effect
of target-flanker spacing on crowding in
multi-element stimulus arrays. We show that
increasing the average distance between the target
and the flankers does not always decrease the amount
of crowding but can even sometimes increase it. We
suggest that the regularity of inter-element spacing
plays an important role in determining the strength
of crowding: regular spacing leads to the perception
of a single, coherent, texture-like stimulus, making
judgments about the individual elements difficult.},
URL = {http://www.journalofvision.org/content/10/10/17.abstract},
eprint = {http://www.journalofvision.org/content/10/10/17.full.pdf+html}
doi = {10.1167/10.10.17}
}
Saarela, T. P. & Herzog, M. H. (2009). Size tuning
and contextual modulation of backward contrast
masking. Journal of Vision, 9(11):21, 1-12.
•
[Link to
article]
[BibTeX reference | .bib-file]
@article{Saarela_Herzog_2009,
author = {Saarela, T. P. and Herzog, M. H.},
title = {Size tuning and contextual modulation of backward contrast masking},
journal = {Journal of Vision},
issn = {1534-7362},
volume = {9},
number = {11},
pages = {1--12},
year = {2009},
month = {10},
abstract = {The strength of contrast masking depends not only on
spatial but also on temporal parameters. In a
previous study (T. P. Saarela & M. H. Herzog, 2008),
we showed that the detection of a briefly presented
Gabor patch is most strongly impaired when an
iso-oriented grating mask immediately follows the
Gabor and that this masking effect is relieved when
a surround is added to the mask. Here, we studied
the spatial characteristics of this backward masking
effect. Gradually changing the size of the
iso-oriented masking grating changes contrast
detection thresholds in a non-monotonic way that can
be explained in terms of contrast-dependent spatial
summation and inhibition. However, these spatial
interactions seem only to take place when the mask
is a uniform grating. When the mask is divided into
a small center and a larger surround by changing the
surround parameters or by adding a small gap,
masking is as strong as with the small center mask
only. We suggest that spatial interactions are
weaker or even absent when the stimulus elements are
perceptually segregated.},
keywords = {contrast masking, temporal processing, surround suppression, contextual modulation},
url = {http://journalofvision.org/9/11/21/},
eprint = {http://journalofvision.org/9/11/21/Saarela-2009-jov-9-11-21.pdf}
}
Saarela, T. P., Sayim, B, Westheimer, G., & Herzog,
M. H. (2009). Global stimulus configuration modulates
crowding. Journal of Vision, 9(2):5,
1-11.
•
[Link to
article]
[BibTeX reference | .bib-file]
@article{Saarela_etal_2009,
author = {Saarela, T. P. and Sayim, B. and Westheimer, G. and Herzog, M. H.},
title = {Global stimulus configuration modulates crowding},
journal = {Journal of Vision},
year = {2009},
volume = {9},
pages = {1--11},
number = {2},
month = {2},
abstract = {In crowding, neighboring elements impair the perception
of a peripherally presented target. Crowding is
often regarded to be a consequence of spatial
pooling of information that leads to the perception
of textural wholes. We studied the effects of
stimulus configuration on crowding using Gabor
stimuli. In accordance with previous studies,
contrast and orientation discrimination of a Gabor
target were impaired in the presence of flanking
Gabors of equal length. The stimulus configuration
was then changed (1) by making the flankers either
shorter or longer than the target or (2) by
constructing each flanker from two or three small
Gabors. These simple configural changes greatly
reduced or even abolished crowding, even though the
orientation, spatial frequency, and phase of the
stimuli were unchanged. The results challenge simple
pooling explanations for crowding. We propose that
crowding is weak whenever the target stands out from
the stimulus array and strong when the target groups
with the flanking elements to form a coherent
texture.},
eprint = {http://journalofvision.org/9/2/5/Saarela-2009-jov-9-2-5.pdf},
issn = {1534-7362},
keywords = {crowding, perceptual organization, spatial vision, detection/discrimination},
url = {http://journalofvision.org/9/2/5/}
}
Saarela, T. P. & Herzog, M. H. (2008). Time-course and surround
modulation of contrast masking in human vision. Journal of
Vision, 8(3):23,
1-10.
•
[Link to
article]
[BibTeX reference | .bib-file]
@article{Saarela_Herzog_2008,
author = {Saarela, T. P. and Herzog, M. H.},
title = {Time-course and surround modulation of contrast masking in human vision},
journal = {Journal of Vision},
year = {2008},
volume = {8},
pages = {1--10},
number = {3},
month = {3},
abstract = {Neural and perceptual responses to a visual stimulus can
be suppressed by the addition of both spatially
overlapping and spatially adjacent contextual
stimuli. We investigated the temporal
characteristics of these suppressive interactions in
psychophysical contrast masking experiments using
Gabor and grating stimuli with a spatial frequency
of 4 cycles per degree. We found that the time
course of masking strongly depended on mask
orientation. Most interestingly, masking by a
spatially overlaid, iso-oriented mask was strongest
when the target was presented immediately before or
immediately after the mask. This masking was
transient, presumably caused by the neural responses
to mask onset and offset. Adding a surround to the
mask modulated the backward masking effect, but only
when the target and the central mask were
iso-oriented. Our results provide evidence for a
surround suppression mechanism that affected the
transient responses to the mask onset, but not the
responses to the mask offset. Together, these
results demonstrate how the effects of spatial
context in visual processing critically depend on
stimulus timing.},
eprint = {http://journalofvision.org/8/3/23/Saarela-2008-jov-8-3-23.pdf},
issn = {1534-7362},
keywords = {temporal processing, surround suppression, contextual modulation,
Gabors},
url = {http://journalofvision.org/8/3/23/}
}
Olkkonen, K.M, Saarela, T.P., & Allred, S.R. (2015). Perception-memory interactions reveal a computa-
tional strategy for perceptual constancy. Journal of Vision, In revision.
Saarela, T.P., Manassi, M., & Herzog, M.H.H. (in
preparation). Effect of TMS on visual signal detection is a result
of both noise and signal suppression.
Saarela, T. P, Mattar, M. G., & Olkkonen, M. (in
preparation). ShapeToolbox: Generating parametric 3D shapes for
visual perception and cognition experiments.