1,721,005 research outputs found
Understanding Misperceived Size through Assimilation in a Novel Illusion: The Binding Ring
Get PDFThe University of Nevada, Reno Libraries will promptly respond to removal requests related to content that violates intellectual property laws, data protections, or has been uploaded without creator consent. Takedown notices should be directed to our ScholarWolf team ([email protected]) with information about the object, including its full URL and the nature of your complaint.How do we perceive the size of objects? This research attempts answer a small part of that question by describing and quantifying the binding ring illusion, a novel (and previously uncharacterized) illusion of misperceived size. Following the establishment of the binding ring as a legitimate size illusion, experiments were performed in an attempt to identify what visual processing stream mechanisms were responsible for the illusion and further, to obtain any information as to the relative whereabouts of said mechanism(s) in the visual processing stream. These experiments were performed because many processing mechanisms of the visual stream (and their relative location therein), especially those in the relatively ‘high’ portion of the visual stream, are very poorly understood. The results of the study gave three primary results: first, the binding ring illusion occurs primarily through a process of assimilation; second, this assimilation process is heavily influenced by a process of perceptual unification; and third, the mechanisms of assimilation and unification are likely located relatively high in the visual processing stream, very likely occurring after spatial frequency integration and either after or during the creation of global shape representations
The maintenance and disambiguation of object representations depend upon feature contrast within and between objects
No full textThe brain processes many aspects of the visual world separately and in parallel, yet we perceive a unified world populated by objects. In order to create such a "bound" percept, the visual system must construct object-centered representations out of separate features and then maintain the representations across changes in space and time. Here, we examine the role of features themselves in maintaining and disambiguating the representations of the objects to which they belong. In three experiments, we measure how the perceived motion of two objects traversing ambiguous trajectories is affected by the contrast between the features and surrounding fields, by the contrast between features, and by changes to orientation of texture within objects. We report that the maintenance and disambiguation of object representations depend on the contrast of the features relative to their surrounds and on the extent of feature differences between the two objects. These feature dependencies indicate that object representation relies on relative response to many stimulus dimensions
Six is Sapphire, but is Sapphire Six? Bidirectionality and Numerosity in Grapheme-Color Synesthesia
No full textThe University of Nevada, Reno Libraries will promptly respond to removal requests related to content that violates intellectual property laws, data protections, or has been uploaded without creator consent. Takedown notices should be directed to our ScholarWolf team ([email protected]) with information about the object, including its full URL and the nature of your complaint.In grapheme-color synesthesia, numbers and letters create a color experience that is consistent, automatic, and unique to each synesthete. Recent studies have examined the way viewing graphemes elicits colors as well as the possibility of bidirectional synesthesia, in which viewing colors may elicit graphemes in the minds of synesthetes (Dixon, Smilek, Cudahy, & Merikle, 2000). This thesis addresses the issue of bidirectionality to see if specific colors elicit the information represented by graphemes in a manner that is cognitively accessible to the synesthete observer. Using psychophysics and event related potential (ERP) waveforms, we found bidirectional synesthesia to exist, as evidenced by synethetes’ ability to accurately complete an arithmetic verification task in which some or all graphemes were replaced with patches of color that matched the synsethetes’ grapheme associations. Synesthete reaction times were just as fast for trials with a color solution as grapheme solution, and were comparable to control participants’ reaction times. The ERP results from showed that the manner in which synesthetes visually process both numbers and colors differs from that of non-synesthetes, with each synesthete showing a wave pattern distinct from controls and from each other. This research adds a crucial piece to the puzzle of how both synesthesia and numerical concepts are processed in the brain, and includes the first study to date that looks at ERP waveforms of synesthetes while performing an arithmetic task requiring bidirectional synesthesia
Human electrophysiological correlates of visual working memory set-size effects at encoding
No full textThe ability to encode, store, and retrieve visually perceived objects is referred to as visual working memory (VWM). Although crucial for many cognitive processes, previous research has found VWM to be strictly capacity limited. This capacity limitation is observable in the set size effect: the ability to successfully report items in VWM asymptotes at a small number of items. Research into the neural correlates of set size effects and the VWM capacity limitation in general has largely focused on the maintenance period of VWM. However, we previously reported that neural resources allocated to individual items during VWM encoding correspond to successful VWM performance. Here we expand upon those findings by investigating neural correlates of set size during VWM encoding. We hypothesized that neural signatures of encoding-related VWM capacity limitations should be differentiable as a function of set size. We tested our hypothesis using High Density Electroencephalography (HD-EEG) to analyze frequency components evoked by flickering target items in VWM displays of set size 2 or 4. Across frontal and occipital-parietal electrodes, set size modulated the amplitude of the 1st and 2nd harmonic frequencies corresponding to correctly recognized targets. Frontal sites exhibited the most robust effects for the 2nd harmonic (set size 2 > set size 4). These results are consistent with a capacity limited VWM resource at encoding that is distributed across the items in a VWM display. This neural set size effect supports the view that VWM capacity limitations begin with encoding related processe
Quantification of a Novel Illusion: Flicker-Induced Induced Motion
Get PDFThe University of Nevada, Reno Libraries will promptly respond to removal requests related to content that violates intellectual property laws, data protections, or has been uploaded without creator consent. Takedown notices should be directed to our ScholarWolf team ([email protected]) with information about the object, including its full URL and the nature of your complaint.Visual illusions are often studied and analyzed to better understand the neural basis of perception. This project aims to quantify flicker-induced induced motion (FLIIM), a newly discovered form of induced motion that causes a stationary object to appear to move when displayed with other moving objects only when all of the objects are flickering. The results revealed that the flicker rate at which FLIIM is the strongest is 2 Hz and that FLIIM gets weaker as the flicker rate increases. The results also revealed that FLIIM is strongest in parafoveal vision and gets weaker in foveal vision. Finally, using isoluminant stimuli, it was determined that FLIIM occurs in second-order motion perception. These findings help refine future models of motion perception and other models that utilize flickering stimuli
Color of Music: An Investigation of Musical Timbre and Color Association
Get PDFThe University of Nevada, Reno Libraries will promptly respond to removal requests related to content that violates intellectual property laws, data protections, or has been uploaded without creator consent. Takedown notices should be directed to our ScholarWolf team ([email protected]) with information about the object, including its full URL and the nature of your complaint.In the world of music, the metaphor “the color of music” has been vastly used to describe characteristics of sound such as tone quality, pitch, and timbre. Timbre can be described as a mixture of frequencies including the fundamental pitch that makes up what we hear when music is played by a particular instrument. While this notion that timbre evokes different color associations is not necessarily a new idea, research is limited outside of experiments based on pitch and other various musical characteristics. This study investigated color association solely based on musical instrument differentiation, or timbre as well as assessing the level of musical experience and training of each subject who participated. Three experiments were utilized including instrument images and sounds with the resulting duty of choosing a color on a color wheel. Findings contributed to the popular knowledge base of music and the brain by signifying a possible, though not well-defined perceptual correlate between musical timbre and color association. Based on the results obtained, the scientific vindication and perceptual basis for the continued use of the metaphor “the color of music” was tentatively upheld based on individual experience, but also signified a need for much more in depth research in timbre processing
The Effects of Motion on Perceived Size and Other Perceptual Processes
Get PDFOptical illusions provide important insights into how we process visual information and illusions that alter the perceived size of an object are a valuable tool to study size perception. Studied for over a century, the classic size illusions have informed us about the complex mechanisms underlying how our brains derive the experience of how big or small objects appear to be. However, these illusions have all been static in nature and thus have ignored motion’s effect on size perception. This review discusses observations of novel dynamic versions of these illusions. Motion has a profound impact on the strength of the illusions tested, with added motion typically creating a stronger effect. Some dynamic versions of these images create an illusion twice as strong as the classic static version. Motion-related manipulations lead to uncertainty in the image size representation of the target, specifically due to added noise at the level of retinal input. We propose a hypothesis that each visual cue involved in size perception is reweighted based on the level of precision or uncertainty in their neural representation. Thus, more weight is given to contextual information when the stimulus and/or eye is moving. Biologically accurate models of size perception need to be able to account for the observed effects of motion
Distinct effects of contour smoothness and observer bias on visual persistence
No full textStable object perception relies on persistent yet temporary neural representations under constantly fluctuating stimulus conditions. The mechanisms by which such representations are formed and maintained are not fully understood but presumably involve interplay between early and higher-tier visual cortical mechanisms. Here we show that the visual persistence of highly camouflaged contours is based on the persistent operation of mechanisms sensitive to contour smoothness, which we dissociate from individual differences in response bias. Our results are consistent with existing models of visual cortical processing that predict persistent contour perception, which until now has not been studied systematically in relation to contour integration. We argue that the surprisingly long duration of contour persistence is in part due to response bias but that the strong modulatory effects of contour smoothness on persistence indicate sustained reverberation of a contour binding mechanism in visual cortex, a unique type of short-term visual memory that supports perceptual continuity
Parietal contributions to visual working memory depend on task difficulty
Get PDFThe nature of parietal contributions to working memory (WM) remain poorly understood but of considerable interest. We previously reported that posterior parietal damage selectively impaired WM probed by recognition (Berryhill & Olson, 2008a). Recent studies provided support using a neuromodulatory technique, transcranial direct current stimulation (tDCS) applied to the right parietal cortex (P4). These studies confirmed parietal involvement in WM because parietal tDCS altered WM performance: anodal current tDCS improved performance in a change detection task, and cathodal current tDCS impaired performance on a sequential presentation task. Here, we tested whether these complementary results were due to different degrees of parietal involvement as a function of WM task demands, WM task difficulty and/or participants' WM capacity. In Experiment 1, we applied cathodal and anodal tDCS to the right parietal cortex and tested participants on both previously used WM tasks. We observed an interaction between tDCS (anodal, cathodal), WM task difficulty and participants' WM capacity. When the WM task was difficult, parietal stimulation (anodal or cathodal) improved WM performance selectively in participants with high WM capacity. In the low WM capacity group, parietal stimulation (anodal or cathodal) impaired WM performance. These nearly equal and opposite effects were only observed when the WM task was challenging, as in the change detection task. Experiment 2 probed the interplay of WM task difficulty and WM capacity in a parametric manner by varying set size in the WM change detection task. Here, the effect of parietal stimulation (anodal or cathodal) on the high WM capacity group followed a linear function as WM task difficulty increased with set size. The low WM capacity participants were largely unaffected by tDCS. These findings provide evidence that parietal involvement in WM performance depends on both WM capacity and WM task demands. We discuss these findings in terms of alternative WM strategies employed by low and high WM capacity individuals. We speculate that low WM capacity individuals do not recruit the posterior parietal lobe for WM tasks as efficiently as high WM capacity individuals. Consequently, tDCS provides greater benefit to individuals with high WM capacity
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