2,348 research outputs found
Global/local processing in incidental perception of hierarchical structure
The goal of the current thesis is to provide a framework for investigating and understanding visual processing of hierarchical structure (i.e., local parts nested in global wholes, such as trees nested in forests) under incidental processing conditions—that is, where processing of information at global and local levels is both uninformative (cannot aid task performance) and task-irrelevant (need not be processed to perform the task). To do so, a novel method combining two widely-used paradigms (spatial cueing and compound stimulus paradigms) is used for implicitly probing observers’ perceptual representations over the course of processing. This compound arrow cueing paradigm was used in five experiments to address a series of objectives. First, which level (global or local) is more dominant in the evolution of a percept? Relatedly, is the temporal structuring of global and local processing fixed or flexible? And what is the time course of level-specific advantages—do they occur earlier or later in the course of processing, and do they follow a transient or protracted time course? Finally, what controls level-specific selection (sensory, perceptual, and/or attentional factors)? The results of the five experiments addressing these issues contribute to a greater understanding of visual perception by elucidating the nature of global and local processing under incidental processing conditions.
Advisor: Michael D. Dod
Global/local processing in incidental perception of hierarchical structure
The goal of the current thesis is to provide a framework for investigating and understanding visual processing of hierarchical structure (i.e., local parts nested in global wholes, such as trees nested in forests) under incidental processing conditions—that is, where processing of information at global and local levels is both uninformative (cannot aid task performance) and task-irrelevant (need not be processed to perform the task). To do so, a novel method combining two widely-used paradigms (spatial cueing and compound stimulus paradigms) is used for implicitly probing observers’ perceptual representations over the course of processing. This compound arrow cueing paradigm was used in five experiments to address a series of objectives. First, which level (global or local) is more dominant in the evolution of a percept? Relatedly, is the temporal structuring of global and local processing fixed or flexible? And what is the time course of level-specific advantages—do they occur earlier or later in the course of processing, and do they follow a transient or protracted time course? Finally, what controls level-specific selection (sensory, perceptual, and/or attentional factors)? The results of the five experiments addressing these issues contribute to a greater understanding of visual perception by elucidating the nature of global and local processing under incidental processing conditions.
Advisor: Michael D. Dod
Which way is which? Examining symbolic control of attention with compound arrow cues
Spatial symbols can generate attentional biases toward peripheral locations compatible with the symbol’s meaning. An important question concerns how one symbol is selected when competing symbols are present. Studies examining this issue for spatially distinct symbols have suggested that selection depends on the task goals. In the present study, we examined whether the influence of competing symbolic stimuli (arrows) at different levels of structure on attentional control also depends on the task goals. Participants made simple detection responses to a peripheral target preceded by a spatially uninformative compound arrow (global arrow composed of local arrows). In addition, participants were required to perform a secondary task in which they matched the orientation of the global arrow (global task) or the location of a uniquely colored local arrow (local task) to a test display presented immediately following a detection response. When the global and local arrows pointed at opposite locations, a local cueing effect emerged in the local task, and a global cueing effect in the global task, indicating that the task goals influenced the selection of the level of structure. However, when the local level was spatially neutral (global arrow, local rectangles), a cueing effect was observed independent of task, and when the global level was spatially neutral (global rectangle, local arrows), a cueing effect was observed in the local task only, suggesting that global processing was obligatory and local processing optional. These findings suggest that attentional effects triggered by the global level are more strongly reflexive than those triggered by the local level
Emotion moderates the association between \u3ci\u3eHTR2A\u3c/i\u3e (rs6313) genotype and antisaccade latency
The serotonin system is heavily involved in cognitive and emotional control processes. Previous work has typically investigated this system’s role in control processes separately for cognitive and emotional domains, yet it has become clear the two are linked. The present study, therefore, examined whether variation in a serotonin receptor gene (HTR2A, rs6313) moderated effects of emotion on inhibitory control. An emotional antisaccade task was used in which participants looked toward (prosaccade) or away (antisaccade) from a target presented to the left or right of a happy, angry, or neutral face. Overall, antisaccade latencies were slower for rs6313 C allele homozygotes than T allele carriers, with no effect of genotype on prosaccade latencies. Thus, C allele homozygotes showed relatively weak inhibitory control but intact reflexive control. Importantly, the emotional stimulus was either present during target presentation (overlap trials) or absent (gap trials). The gap effect (slowed latency in overlap versus gap trials) in antisaccade trials was larger with angry versus neutral faces in C allele homozygotes. This impairing effect of negative valence on inhibitory control was larger in C allele homozygotes than T allele carriers, suggesting that angry faces disrupted/ competed with the control processes needed to generate an antisaccade to a greater degree in these individuals. The genotype difference in the negative valence effect on antisaccade latency was attenuated when trial N-1 was an antisaccade, indicating top-down regulation of emotional influence. This effect was reduced in C/C versus T/_ individuals, suggesting a weaker capacity to downregulate emotional processing of task-irrelevant stimuli
Tracking TCRĂź sequence clonotype expansions during antiviral therapy using high-throughput sequencing of the hypervariable region
To maintain a persistent infection viruses such as hepatitis C virus (HCV) employ a range of mechanisms that subvert protective T cell responses. The suppression of antigen-specific T cell responses by HCV hinders efforts to profile T cell responses during chronic infection and antiviral therapy. Conventional methods of detecting antigen-specific T cells utilize either antigen stimulation (e.g., ELISpot, proliferation assays, cytokine production) or antigen-loaded tetramer staining. This limits the ability to profile T cell responses during chronic infection due to suppressed effector function and the requirement for prior knowledge of antigenic viral peptide sequences. Recently, high-throughput sequencing (HTS) technologies have been developed for the analysis of T cell repertoires. In the present study, we have assessed the feasibility of HTS of the TCRβ complementarity determining region (CDR)3 to track T cell expansions in an antigen-independent manner. Using sequential blood samples from HCV-infected individuals undergoing antiviral therapy, we were able to measure the population frequencies of >35,000 TCRβ sequence clonotypes in each individual over the course of 12 weeks. TRBV/TRBJ gene segment usage varied markedly between individuals but remained relatively constant within individuals across the course of therapy. Despite this stable TRBV/TRBJ gene segment usage, a number of TCRβ sequence clonotypes showed dramatic changes in read frequency. These changes could not be linked to therapy outcomes in the present study; however, the TCRβ CDR3 sequences with the largest fold changes did include sequences with identical TRBV/TRBJ gene segment usage and high junction region homology to previously published CDR3 sequences from HCV-specific T cells targeting the HLA-B*0801-restricted 1395HSKKKCDEL1403 and HLA-A*0101-restricted 1435ATDALMTGY1443 epitopes. The pipeline developed in this proof of concept study provides a platform for the design of future experiments to accurately address the question of whether T cell responses contribute to SVR upon antiviral therapy. This pipeline represents a novel technique to analyze T cell dynamics in situations where conventional antigen-dependent methods are limited due to suppression of T cell functions and highly diverse antigenic sequences
Life expectancy of persons receiving combination antiretroviral therapy in low-income countries: a cohort analysis from Uganda
Little is known about the effect of combination antiretroviral therapy (cART) on life expectancy in sub-Saharan Africa
The Politics of the Face-in-the-Crowd
Recent work indicates that the more conservative one is, the faster one is to fixate on negative stimuli, whereas the less conservative one is, the faster one is to fixate on positive stimuli. The present series of experiments used the face-in-the-crowd paradigm to examine whether variability in the efficiency with which positive and negative stimuli are detected underlies such speed differences. Participants searched for a discrepant facial expression (happy or angry) amid a varying number of neutral distractors (Experiments 1 and 4). A combination of response time and eye movement analyses indicated that variability in search efficiency explained speed differences for happy expressions, whereas variability in post-selectional processes explained speed differences for angry expressions. These results appear to be emotionally mediated as search performance did not vary with political temperament when displays were inverted (Experiment 2) or when controlled processing was required for successful task performance (Experiment 3). Taken together, the present results suggest political temperament is at least partially instantiated by attentional biases for emotional material
School, Community and Clinical Psychology Training and Working together in the Interdisciplinary School Mental Health Field
Effects of task and task-switching on temporal inhibition of return, facilitation of return, and saccadic momentum during scene viewing
During scene viewing, saccades directed toward a recently fixated location tend to be delayed relative to saccades in other directions (“delay effect”), an effect attributable to inhibition-of-return (IOR) and/or saccadic momentum (SM). Previous work indicates this effect may be task-specific, suggesting that gaze control parameters are task-relevant and potentially affected by task-switching. Accordingly, the present study investigated task-set control of gaze behavior using the delay effect as a measure of task performance. The delay effect was measured as the effect of relative saccade direction on preceding fixation duration. Participants were cued on each trial to perform either a search, memory, or rating task. Tasks were performed either in pure-task or mixed-task blocks. This design allowed separation of switch-cost and mixing-cost. The critical result was that expression of the delay effect at 2-back locations was reversed on switch versus repeat trials such that return was delayed in repeat trials but speeded in switch trials. This difference between repeat and switch trials suggests that gaze-relevant parameters may be represented and switched as part of a task-set. Existing and new tests for dissociating IOR and SM accounts of the delay effect converged on the conclusion that the delay at 2-back locations was due to SM, and that task-switching affects SM. Additionally, the new test simultaneously replicated non-corroborating results in the literature regarding facilitation-of-return (FOR), which confirmed its existence and showed that FOR is “reversed” SM that occurs when preceding and current saccades are both directed toward the 2-back location
Obama cares about visuo-spatial attention: Perception of political figures moves attention and determines gaze direction
Processing an abstract concept such as political ideology by itself is difficult but becomes easier when a background situation contextualizes it. Political ideology within American politics, for example, is commonly processed using space metaphorically, i.e., the political “left” and “right” (referring to Democrat and Republican views, respectively), presumably to provide a common metric to which abstract features of ideology can be grounded and understood. Commonplace use of space as metaphor raises the question of whether an inherently non-spatial stimulus (e.g., picture of the political “left” leader, Barack Obama) can trigger a spatially-specific response (e.g., attentional bias toward “left” regions of the visual field). Accordingly, pictures of well-known Democrats and Republicans were presented as central cues in peripheral target detection (Experiment 1) and saccadic free-choice (Experiment 2) tasks to determine whether perception of stimuli lacking a direct association with physical space nonetheless induce attentional and oculomotor biases in the direction compatible with the ideological category of the cue (i.e., Democrat/left and Republican/right). In Experiment 1, target detection following presentation of a Democrat (Republican) was facilitated for targets appearing to the left (right). In Experiment 2, participants were more likely to look left (right) following presentation of a Democrat (Republican). Thus, activating an internal representation of political ideology induced a shift of attention and biased choice of gaze direction in a spatially-specific manner. These findings demonstrate that the link between conceptual processing and spatial attention can be totally arbitrary, with no reference to physical or symbolic spatial information
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