9 research outputs found
Large crowding zones in peripheral vision for briefly presented stimuli
YesWhen a target is flanked by distractors, it becomes more
difficult to identify. In the periphery, this crowding effect
extends over a wide range of target-flanker separations,
called the spatial extent of interaction (EoI). A recent
study showed that the EoI dramatically increases in size
for short presentation durations (Chung & Mansfield,
2009). Here we investigate this duration-EoI relation in
greater detail and show that (a) it holds even when
visibility of the unflanked target is equated for different
durations, (b) the function saturates for durations
shorter than 30 to 80 ms, and (c) the largest EoIs
represent a critical spacing greater than 50% of
eccentricity. We also investigated the effect of same or
different polarity for targets and flankers across different
presentation durations. We found that EoIs for target
and flankers having opposite polarity (one white, the
other black) show the same temporal pattern as for
same polarity stimuli, but are smaller at all durations by
29% to 44%. The observed saturation of the EoI for shortduration
stimuli suggests that crowding follows the locus
of temporal integration. Overall, the results constrain
theories that map crowding zones to fixed spatial
extents or to lateral connections of fixed length in the
cortex.This study was supported by the ERC POSITION 324070 (PC) and a visiting professorship to Anglia Ruskin University from the Leverhulme Trust (HEB)
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Stream specificity and asymmetries in feature binding and content-addressable access in visual encoding and memory
YesHuman memory is content addressable—i.e., contents of
the memory can be accessed using partial information
about the bound features of a stored item. In this study,
we used a cross-feature cuing technique to examine how
the human visual system encodes, binds, and retains
information about multiple stimulus features within a
set of moving objects. We sought to characterize the
roles of three different features (position, color, and
direction of motion, the latter two of which are
processed preferentially within the ventral and dorsal
visual streams, respectively) in the construction and
maintenance of object representations. We investigated
the extent to which these features are bound together
across the following processing stages: during stimulus
encoding, sensory (iconic) memory, and visual shortterm
memory. Whereas all features examined here can
serve as cues for addressing content, their effectiveness
shows asymmetries and varies according to cue–report
pairings and the stage of information processing and
storage. Position-based indexing theories predict that
position should be more effective as a cue compared to
other features. While we found a privileged role for
position as a cue at the stimulus-encoding stage, position
was not the privileged cue at the sensory and visual
short-term memory stages. Instead, the pattern that
emerged from our findings is one that mirrors the
parallel processing streams in the visual system. This
stream-specific binding and cuing effectiveness
manifests itself in all three stages of information
processing examined here. Finally, we find that the Leaky
Flask model proposed in our previous study is applicable
to all three features
Application of zebrafish oculomotor behavior to model human disorders
To ensure high acuity vision, eye movements have to be controlled with astonishing precision by the oculomotor system. Many human diseases can lead to abnormal eye movements, typically of the involuntary oscillatory eye movements type called nystagmus. Such nystagmus can be congenital (infantile) or acquired later in life. Although the resulting eye movements are well characterized, there is only little information about the underlying etiology. This is in part owing to the lack of appropriate animal models. In this review article, we describe how the zebrafish with its quick maturing visual system can be used to model oculomotor pathologies. We compare the characteristics and assessment of human and zebrafish eye movements. We describe the oculomotor properties of the zebrafish mutant belladonna, which has non-crossing optical fibers, and is a particularly informative model for human oculomotor deficits. This mutant displays a reverse optokinetic response, spontaneous oscillations that closely mimic human congenital nystagmus and abnormal motor behavior linked to circular vection
Pines
Pinus is the most important genus within the Family Pinaceae and also within the gymnosperms by the number of species (109 species recognized by Farjon 2001) and by its contribution to forest ecosystems. All pine species are evergreen trees or shrubs. They are widely distributed in the northern hemisphere, from tropical areas to northern areas in America and Eurasia. Their natural range reaches the equator only in Southeast Asia. In Africa, natural occurrences are confined to the Mediterranean basin. Pines grow at various elevations from sea level (not usual in tropical areas) to highlands. Two main regions of diversity are recorded, the most important one in Central America (43 species found in Mexico) and a secondary one in China. Some species have a very wide natural range (e.g., P. ponderosa, P. sylvestris). Pines are adapted to a wide range of ecological conditions: from tropical (e.g., P. merkusii, P. kesiya, P. tropicalis), temperate (e.g., P. pungens, P. thunbergii), and subalpine (e.g., P. albicaulis, P. cembra) to boreal (e.g., P. pumila) climates (Richardson and Rundel 1998, Burdon 2002). They can grow in quite pure stands or in mixed forest with other conifers or broadleaved trees. Some species are especially adapted to forest fires, e.g., P. banksiana, in which fire is virtually essential for cone opening and seed dispersal. They can grow in arid conditions, on alluvial plain soils, on sandy soils, on rocky soils, or on marsh soils. Trees of some species can have a very long life as in P. longaeva (more than 3,000 years)