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    ABSTRACT: Curvature is a highly informative visual cue for shape perception and object recognition. We introduce a novel illusion-the Lemon Illusion-in which subtle illusory curvature is perceived along contour regions that are devoid of physical curvature. We offer several perceptual demonstrations and observations that lead us to conclude that the Lemon Illusion is an instance of a more general illusory curvature phenomenon, one in which the presence of contour curvature discontinuities lead to the erroneous extension of perceived curvature. We propose that this erroneous extension of perceived curvature results from the interaction of neural mechanisms that operate on spatially local contour curvature signals with higher-tier mechanisms that serve to establish more global representations of object shape. Our observations suggest that the Lemon Illusion stems from discontinuous curvature transitions between rectilinear and curved contour segments. However, the presence of curvature discontinuities is not sufficient to produce the Lemon Illusion, and the minimal conditions necessary to elicit this subtle and insidious illusion are difficult to pin down.
    Frontiers in Human Neuroscience 02/2015; 9:95. DOI:10.3389/fnhum.2015.00095
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    ABSTRACT: The Ebbinghaus illusion is a classic example of the influence of a contextual surround on the perceived size of an object. Here, we introduce a novel variant of this illusion called the Dynamic Ebbinghaus illusion in which the size and eccentricity of the surrounding inducers modulates dynamically over time. Under these conditions, the size of the central circle is perceived to change in opposition with the size of the inducers. Interestingly, this illusory effect is relatively weak when participants are fixating a stationary central target, less than half the magnitude of the classic static illusion. However, when the entire stimulus translates in space requiring a smooth pursuit eye movement to track the target, the illusory effect is greatly enhanced, almost twice the magnitude of the classic static illusion. A variety of manipulations including target motion, peripheral viewing, and smooth pursuit eye movements all lead to dramatic illusory effects, with the largest effect nearly four times the strength of the classic static illusion. We interpret these results in light of the fact that motion-related manipulations lead to uncertainty in the image size representation of the target, specifically due to added noise at the level of the retinal input. We propose that the neural circuits integrating visual cues for size perception, such as retinal image size, perceived distance, and various contextual factors, weight each cue according to the level of noise or uncertainty in their neural representation. Thus, more weight is given to the influence of contextual information in deriving perceived size in the presence of stimulus and eye motion. Biologically plausible models of size perception should be able to account for the reweighting of different visual cues under varying levels of certainty.
    Frontiers in Human Neuroscience 02/2015; 9:77. DOI:10.3389/fnhum.2015.00077
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    ABSTRACT: Research studies in psychology typically use two-dimensional (2D) images of objects as proxies for real-world three-dimensional (3D) stimuli. There are, however, a number of important differences between real objects and images that could influence cognition and behavior. Although human memory has been studied extensively, only a handful of studies have used real objects in the context of memory and virtually none have directly compared memory for real objects vs. their 2D counterparts. Here we examined whether or not episodic memory is influenced by the format in which objects are displayed. We conducted two experiments asking participants to freely recall, and to recognize, a set of 44 common household objects. Critically, the exemplars were displayed to observers in one of three viewing conditions: real-world objects, colored photographs, or black and white line drawings. Stimuli were closely matched across conditions for size, orientation, and illumination. Surprisingly, recall and recognition performance was significantly better for real objects compared to colored photographs or line drawings (for which memory performance was equivalent). We replicated this pattern in a second experiment comparing memory for real objects vs. color photos, when the stimuli were matched for viewing angle across conditions. Again, recall and recognition performance was significantly better for the real objects than matched color photos of the same items. Taken together, our data suggest that real objects are more memorable than pictorial stimuli. Our results highlight the importance of studying real-world object cognition and raise the potential for applied use in developing effective strategies for education, marketing, and further research on object-related cognition.
    Frontiers in Human Neuroscience 10/2014; 8:1. DOI:10.3389/fnhum.2014.00837
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    ABSTRACT: The popularity of non-invasive brain stimulation techniques in basic, commercial, and applied settings grew tremendously over the last decade. Here, we focus on one popular neurostimulation method: transcranial direct current stimulation (tDCS). Many assumptions regarding the outcomes of tDCS are based on the results of stimulating motor cortex. For instance, the primary motor cortex is predictably suppressed by cathodal tDCS or made more excitable by anodal tDCS. However, wide-ranging studies testing cognition provide more complex and sometimes paradoxical results that challenge this heuristic. Here, we first summarize successful efforts in applying tDCS to cognitive questions, with a focus on working memory (WM). These recent findings indicate that tDCS can result in cognitive task improvement or impairment regardless of stimulation site or direction of current flow. We then report WM and response inhibition studies that failed to replicate and/or extend previously reported effects. From these opposing outcomes, we present a series of factors to consider that are intended to facilitate future use of tDCS when applied to cognitive questions. In short, common pitfalls include testing too few participants, using insufficiently challenging tasks, using heterogeneous participant populations, and including poorly motivated participants. Furthermore, the poorly understood underlying mechanism for long-lasting tDCS effects make it likely that other important factors predict responses. In conclusion, we argue that although tDCS can be used experimentally to understand brain function its greatest potential may be in applied or translational research.
    Frontiers in Psychology 07/2014; 5:800. DOI:10.3389/fpsyg.2014.00800
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    ABSTRACT: Despite implications for theory and treatment, commonality in responding to non-bereavement and bereavement losses are not well explicated. This study identified the factor structure of the three most common responses to bereavement, prolonged grief, posttraumatic stress, and major depression in a bereaved community sample (n=151, 59% female, 68% white) from the U.S. recruited from Amazon's MTurk using a cross-sectional survey design, then cross-validated the structure in samples where people had lost other potentially self-defining roles; one's employment (n=157, 47% female, 69% white) and one's marriage (n=116, 62% female, 80% white). Results indicated that symptoms of prolonged grief, posttraumatic stress, and major depression were distinct factors in the bereaved sample, the three-factor solution was a good fit for the job-loss and divorce samples, and levels of grief in each sample appeared to be best predicted by time since loss and centrality of the loss to one's identity. Limitations include potential sample bias due to convenience sampling, and the cross-sectional design did not allow examination of the stability of factors over time. These results suggest that grief is not a unique response to loss of loved one but instead may be a common phenomenology across types of loss. This implies that facilitating meaningful engagement in self-defining activities that compensate for the disrupting loss might be efficacious in promoting grief resolution without the need for working through individuals' emotional attachment to a specific individual or processing one's emotional responses to the loss.
    Journal of Affective Disorders 06/2014; 161:136-43. DOI:10.1016/j.jad.2014.03.018
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    ABSTRACT: Alexithymia is a term used to describe individuals who seem unable to experience or at least describe emotions. This paper offers a theoretical interpretation of alexithymia from a radical behaviorist perspective. While there have been attempts to explain the etiology of alexithymia, the current analysis is unique in that it provides direct treatment implications. The pragmatic analysis described focuses on the verbal behavior of individuals rather than looking “inside” for explanations. This is supported by a review of experimental research that has failed to find consistencies among alexithymic individuals’ physiological responding. Descriptions of the various discriminative and consequential stimulus conditions involved in the complex learning histories of individuals that could result in an alexithymic presentation are provided. This analysis helps situate the alexithymia construct in a broader behavior analytic understanding of emotions. Finally this paper outlines implications for assessment and treatment, which involve influencing discriminative and consequential interpersonal stimulus conditions to shape verbal behavior about emotions.
    Journal of Contextual Behavioral Science 04/2014; 3(2). DOI:10.1016/j.jcbs.2014.03.002
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    ABSTRACT: A recent study showed that color synesthetes have increased color sensitivity but impaired motion perception. This is exciting because little research has examined how synesthesia affects basic perceptual processes outside the context of synesthetic experiences. The results suggest that synesthesia broadly impacts perception with greater neural implications than previously considered.
    Trends in Cognitive Sciences 02/2014; 18(5). DOI:10.1016/j.tics.2014.02.002
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    ABSTRACT: Abstract Objective: This study examined the feasibility of a prototype Web-based acceptance and commitment therapy (ACT) program for preventing mental health problems among college students. Participants: Undergraduate first-year students (N = 76) participated between May and November 2011. Methods: Participants were randomized to ACT or a waitlist, with assessments conducted at baseline, posttherapy, and 3-week follow-up. Waitlist participants accessed the program after the second assessment. Results: Program usability/usage data indicated high program acceptability. Significant improvements were found for ACT knowledge, education values, and depression with ACT relative to waitlist. Subgroup analyses indicated that ACT decreased depression and anxiety relative to waitlist among students with at least minimal distress. Within the ACT condition, significant improvements were observed from baseline to 3-week follow-up on all outcome and process measures. Conclusions: Results provide preliminary support for the feasibility of a Web-based ACT prevention program.
    Journal of American College Health 01/2014; 62(1):20-30. DOI:10.1080/07448481.2013.843533
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    ABSTRACT: This study investigated the feasibility of using behavioral activation to treat enduring postbereavement mental health difficulties using a two-arm, multiple baseline design comparing an immediate start group to a delayed start group at baseline, 12-, 24-, and 36-weeks postrandomization. Participants received 12-14 sessions of behavioral activation within a 12-week intervention period starting immediately after the first assessment or after 12weeks for the delayed start group. Prolonged grief, posttraumatic stress, and depression symptoms were assessed as outcomes. Compared with no treatment, behavioral activation was associated with large reductions in prolonged, complicated, or traumatic grief; posttraumatic stress disorder; and depression symptoms in the intent-to-treat analyses. Seventy percent of the completer sample at posttreatment and 75 percent at follow-up responded to treatment with 45 percent at posttreatment and 40 percent at follow-up being classified as evidencing high-end state functioning at 12-week follow-up.
    Behavior therapy 12/2013; 44(4):639-650. DOI:10.1016/j.beth.2013.04.009
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    ABSTRACT: Radiologists must classify and interpret medical images on the basis of visual inspection. We examined how the perception of radiological scans might be affected by common processes of adaptation in the visual system. Adaptation selectively adjusts sensitivity to the properties of the stimulus in current view, inducing an aftereffect in the appearance of stimuli viewed subsequently. These perceptual changes have been found to affect many visual attributes, but whether they are relevant to medical image perception is not well understood. To examine this we tested whether aftereffects could be generated by the characteristic spatial structure of radiological scans, and whether this could bias their appearance along dimensions that are routinely used to classify them. Measurements were focused on the effects of adaptation to images of normal mammograms, and were tested in observers who were not radiologists. Tissue density in mammograms is evaluated visually and ranges from "dense" to "fatty." Arrays of images varying in intermediate levels between these categories were created by blending dense and fatty images with different weights. Observers first adapted by viewing image samples of dense or fatty tissue, and then judged the appearance of the intermediate images by using a texture matching task. This revealed pronounced perceptual aftereffects - prior exposure to dense images caused an intermediate image to appear more fatty and vice versa. Moreover, the appearance of the adapting images themselves changed with prolonged viewing, so that they became less distinctive as textures. These aftereffects could not be accounted for by the contrast differences or power spectra of the images, and instead tended to follow from the phase spectrum. Our results suggest that observers can selectively adapt to the properties of radiological images, and that this selectivity could strongly impact the perceived textural characteristics of the images.
    PLoS ONE 10/2013; 8(10):e76175. DOI:10.1371/journal.pone.0076175
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