Previous studies investigating interactions between spatial attention and numeric stimuli (see SNARC effect) have identified an attentional bias induced by numeric stimuli in accordance with a mental number line model of processing. This processing model attributes orienting effects induced by numeric stimuli to long-term memory structures, such as a left-to-right number system in a given culture. The present study aims to investigate long-term memory may modulate attentional biases induced by the contents in short-term memory. In other words, can simply thinking about number induce spatial biasing effects? In this study, dichotic listening is used to measure of spatial attention in the auditory modality. Subjects were given numeric items to retain in short term memory during the spatial attention task, and prompted to recall the numbers verbally after each trial. Factors of number magnitude, load size, interval size between numbers, and presentation order are analyzed in terms of their effect on auditory spatial orienting. Auditory spatial orienting is assessed through a measure of laterality index – a ratio of left/right ear responses indicating attention as allocated to the left or right side of space. Results demonstrated a clear influence of number magnitude and presentation order on auditory spatial attention, however these effects were highly variable depending on other factors present in each experiment. Overall, results suggest that in addition to SNARC based orienting responses, the orienting effects of items in short term memory on spatial attention may be influenced by novelty, interactions with language, and multiple neural mechanisms responsible for representing quantity information. / acase@tulane.edu

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Doctor of Philosophy / Department of Psychological Sciences / Lester Loschky / Everyday event perception requires us to perceive a nearly constant stream of dynamic information. Although we perceive these events as being continuous, there is ample evidence that we “chunk” our experiences into manageable bits (Zacks & Swallow, 2007). These chunks can occur at fine and coarse grains, with fine event segments being nested within coarse-grained segments. Individual differences in boundary detection are important predictors for subsequent memory encoding and retrieval and are relevant to both normative and pathological spectra of cognition. However, the nature of attention in relation to event structure is not yet well understood. Attention is the process which suppresses irrelevant information while facilitating the extraction of relevant information. Though attentional changes are known to occur around event boundaries, it is still not well understood when and where these changes occur. A newly developed method for measuring attention, the Gaze-Contingent Useful Field of View Task (GC-UFOV; Gaspar et al., 2016; Ringer, Throneburg, Johnson, Kramer, & Loschky, 2016; Ward et al., 2018) provides a means of measuring attention across the visual field (a) in simulated real-world environments and (b) independent of eccentricity-dependent visual constraints. To measure attention, participants performed the GC-UFOV task while watching pre-segmented videos of everyday activities (Eisenberg & Zacks, 2016; Sargent et al., 2013). Attention was probed from 4 seconds prior to 6 seconds after coarse, fine, and non-event boundaries. Afterward, participants’ memories for objects and event order were tested, followed by event segmentation. Attention was predicted to either become impaired (attentional impairment hypothesis), or it was predicted to be broadly distributed at event boundaries and narrowed at event middles (the ambient-to-focal shift hypothesis). The results showed marginal evidence for both attentional impairment and ambient-to-focal shift hypotheses, however model fitness was equal for both models. The results of this study were then used to develop a proposed program of research to further explore the nature of attention during event perception, as well as the ability of these two hypotheses to explain the relationship between attention and memory during real-world event perception.

The Where's Waldo problem concerns how individuals can rapidly scan a scene to detect a target object in it. This dissertation develops the ARTSCAN Search neural model to clarify how brain mechanisms that govern spatial and object attention, spatially-invariant object learning and recognition, reinforcement learning, and eye movement search are coordinated to enable learning and directed search for desired objects at specific locations in a cluttered scene. In the model, interactions from the Where cortical processing stream to the What cortical processing stream modulate invariant category learning of a desired object, whereas interactions from the What cortical processing stream to the Where cortical processing stream support search for the object. In particular, when an invariant object category representation is activated top-down by a cognitive plan or by an active motivational source in the model's What stream, it can shift spatial attention in the Where stream and thereby selectively activate the locations of sought-after object exemplars. These combined What-to-Where and Where-to-What interactions clarify how the brain's solution of the Where's Waldo problem overcomes the complementary deficiencies of What and Where stream processes taken individually by using inter-stream interactions that allow both invariant object recognition and spatially selective attention and action to occur.

Many studies have found that fixating or directing spatial attention to different regions can bias the perception of the Necker cube, but whether this effect of spatial attention is due to attended areas perceived as being closer have yet to be examined. This issue was directly investigated in this study. The stimulus used was the diamond stimulus, containing four occluders and four moving lines that can be perceived as coherent or separate motions. The results of Experiment 1 show that coherent motion was perceived more often under the attending-to-occluders condition than under the attending-to-moving-lines condition, indicating that spatial attention can bias multistable perception. The results of Experiment 2 show that the mean probability of reporting lines behind occluders in small binocular disparities was significantly higher under the attending-to-occluders condition than under the attending-to-lines condition, indicating that spatial attention can make attended areas look slightly closer. The results of Experiments 3 and 4 show that the effect of spatial attention on biasing multistable perception was weakened when there were binocular or monocular depth cues to define the depth relationship between the occluders and the lines. These results are all consistent with the notion that spatial attention can bias multistable perception through affecting depth perception, making attended areas look closer.

Human information processing depends critically on continuous predictions about upcoming events, but the temporal convergence of expectancy-based top-down and input-driven bottom-up streams is poorly understood. We show that, during reading, event-related potentials differ between exposure to highly predictable and unpredictable words no later than 90 ms after visual input. This result suggests an extremely rapid comparison of expected and incoming visual information and gives an upper temporal bound for theories of top-down and bottom-up interactions in object recognition.

Linear mixed models (LMMs) provide a still underused methodological perspective on combining experimental and individual-differences research. Here we illustrate this approach with two-rectangle cueing in visual attention (Egly et al., 1994). We replicated previous experimental cue-validity effects relating to a spatial shift of attention within an object (spatial effect), to attention switch between objects (object effect), and to the attraction of attention toward the display centroid (attraction effect), also taking into account the design-inherent imbalance of valid and other trials. We simultaneously estimated variance/covariance components of subject-related random effects for these spatial, object, and attraction effects in addition to their mean reaction times (RTs). The spatial effect showed a strong positive correlation with mean RT and a strong negative correlation with the attraction effect. The analysis of individual differences suggests that slow subjects engage attention more strongly at the cued location than fast subjects. We compare this joint LMM analysis of experimental effects and associated subject-related variances and correlations with two frequently used alternative statistical procedures

Body schema is indispensable for sensorimotor control and learning, but it remains unclear whether it is associated with cognitive functions. Data from patients with spatial neglect support this view; yet observations in healthy participants are inconsistent. Here I conducted two sets of experiments examining influences of trunk position: the first probed attention and spatial working memory using a change detection task and a two-back task; the second used different versions of the Posner paradigm to examine whether head-on-trunk position governs disengagement of attention. In none of the experiments did I observe that trunk turns altered performance in the left versus right visual field in an ipsiversive fashion as reported in neglect. Nevertheless, I found that trunk-right position improved performance at eccentric locations of the visual field. The data are inconsistent with previous findings of head-on-trunk effects in normal participants. Further studies are required to clarify these discrepancies.

Body schema is indispensable for sensorimotor control and learning, but it remains unclear whether it is associated with cognitive functions. Data from patients with spatial neglect support this view; yet observations in healthy participants are inconsistent. Here I conducted two sets of experiments examining influences of trunk position: the first probed attention and spatial working memory using a change detection task and a two-back task; the second used different versions of the Posner paradigm to examine whether head-on-trunk position governs disengagement of attention. In none of the experiments did I observe that trunk turns altered performance in the left versus right visual field in an ipsiversive fashion as reported in neglect. Nevertheless, I found that trunk-right position improved performance at eccentric locations of the visual field. The data are inconsistent with previous findings of head-on-trunk effects in normal participants. Further studies are required to clarify these discrepancies.

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