No description available.

Yes / We examined whether visual processing mechanisms of the body of conspecifics are different in women and men and whether these rely on westernised socio-cultural ideals and body image concerns. Twenty-four women and 24 men performed a visual discrimination task of upright or inverted images of female or male bodies and faces (Experiment 1) and objects (Experiment 2). In Experiment 1, both groups of women and men showed comparable abilities in the discrimination of upright and inverted bodies and faces. However, the gender of the human stimuli yielded different effects on participants’ performance, so that female faces, and male bodies appeared to be processed less configurally than female bodies and male faces, respectively. Interestingly, the reduction of configural processing for male bodies was significantly predicted by participants’ Body Mass Index (BMI) and their level of internalization of muscularity. Our findings suggest that configural visual processing of bodies and faces in women and men may be linked to a selective attention to detail needed for discriminating salient physical (perhaps sexual) cues of conspecifics. Importantly, BMI and muscularity internalization of beauty ideals may also play a crucial role in this mechanism.

Younger adults’ perception of and attention to facial stimuli are enhanced by positive and negative emotional expressions, with negativity leading to a greater benefit than positivity. Conversely, older adults demonstrate a positivity bias, devoting more attention to positive stimuli and less to negative. It is unclear if age differences in these attentional preferences emerge due to differences in how their perceptual systems respond to positive and negative stimuli. Emotional facial expressions elicit enhanced P1 and N170 components of visually-evoked event-related potentials (ERP) over posterior scalp regions associated with vision. The current study examined the extent to which angry and happy facial expressions evoked differential patterns of P1 and N170 enhancements in younger (n = 21, ages 18-30) and older (n = 20, ages 60-76) adults. Participants were presented with happy, angry, and neutral faces under four instructional conditions: passively view, passively view but consider emotion, categorize emotion, and categorize gender. ERPs were recorded from the posterior scalp electrodes of a 128- channel high density electrode array and were time-locked to the onset of facial stimuli. The recordings were segmented and averaged based on the instructional condition and emotional expression of the stimulus. Analyses of the average P1 and N170 latencies revealed no age differences. Overall, participants displayed larger amplitude P1 and N170 to all stimuli when asked to categorize gender or emotionality. Contrary to expectations, both younger and older adults displayed larger N170 amplitudes for angry and happy expressions relative to neutral ones. Although older adults display a positivity bias in allocating attention to emotional stimuli, in the current study, younger and older adults both displayed an enhanced N170 for emotional faces relative to neutral faces, suggesting that the perceptual systems of younger and older adults are similarly engaged in processing positive and negative facial expressions at early time points.

For human and animal vision, the perception of local visual features can depend on the spatial arrangement of the surrounding visual stimuli. In the earliest stages of visual processing this phenomenon is called surround modulation, where the response of visually selective neurons is influenced by the response of neighboring neurons. Surround modulation has been implicated in numerous important perceptual phenomena, such as contour integration and figure-ground segregation. In cats, one of the major potential neural substrates for surround modulation are lateral connections between cortical neurons in layer 2/3, which typically contains ”complex” cells that appear to combine responses from ”simple” cells in layer 4C. Interestingly, these lateral connections have also been implicated in the development of functional maps in primary visual cortex, such as smooth, well-organized maps for the preference of oriented lines. Together, this evidence suggests a common underlying substrate the lateral interactions in layer 2/3—as the driving force behind development of orientation maps for both simple and complex cells, and at the same time expression of surround modulation in adult animals. However, previously these phenomena have been studied largely in isolation, and we are not aware of a computational model that can account for all of them simultaneously and show how they are related. In this thesis we resolve this problem by building a single, unified computational model that can explain the development of orientation maps, the development of simple and complex cells, and surround modulation. First we build a simple, single-layer model of orientation map development based on ALISSOM, which has more realistic single cell properties (such as contrast gain control and contrast invariant orientation tuning) than its predecessor. Then we extend this model by adding layer 2/3, and show how the model can explain development of orientation maps of both simple and complex cells. As the last step towards a developmental model of surround modulation, we replace Mexican-hat-like lateral connectivity in layer 2/3 of the model with a more realistic configuration based on long-range excitation and short-range inhibitory cells, extending a simpler model by Judith Law. The resulting unified model of V1 explains how orientation maps of simple and complex cells can develop, while individual neurons in the developed model express realistic orientation tuning and various surround modulation properties. In doing so, we not only offer a consistent explanation behind all these phenomena, but also create a very rich model of V1 in which the interactions between various V1 properties can be studied. The model allows us to formulate several novel predictions that relate the variation of single cell properties to their location in the orientation preference maps in V1, and we show how these predictions can be tested experimentally. Overall, this model represents a synthesis of a wide body of experimental evidence, forming a compact hypothesis for much of the development and behavior of neurons in the visual cortex.

M.A.University of the Witwatersrand, Faculty of Humanities (Fine Arts), 2012 / The ‘Bath Series’ (1983-1988) of Jasper Johns shows the artist’s meditation on his oeuvre of the past thirty years, and the examples of his previous works demonstrate his interest in instabilities of visual perception. The latter are activated when the viewer’s expectation to see conventional representational strategies are destabilized, and figure/ground pictorial space, particularly, becomes ambiguous. This first recorded academic study focusing exclusively on the series as a unit, discovers that figure/ground switching, an ‘Ur-Gestalt’ (Gandelman 1989: 209), appears to be a core energy motivating ambiguous pictorial space in Johns’ art, and constitutes the theoretical component of the research. The practical component is a site specific installation which shows some visual and verbal processes and meditates on the perpetual interaction between the eye and the mind, which is a fundamental concern of Johns (Varnedoe 1996b: 245, 257), as well as of myself. The work invites viewers to experience destabilized conventional visual perceptions and to explore, as Johns said, ‘something new’ (Varnedoe 1996a: 17).

Visual processing, though seemingly automatic, is complex. Typical humansprocess objects and faces routinely. Yet, when a disease or disorder disrupts face andobject recognition, the effects are profound. Because of its importance and complexity,visual processing has been the subject of many adult functional imaging studies.However, relatively little is known about the development of the neural organization andunderlying cognitive mechanisms of face and object recognition. The current projectused functional magnetic resonance imaging (fMRI) to identify maturational changes inthe neural substrates of face and object recognition in 5-8 year olds, 9-11 year olds, andadults. A passive face and object viewing task revealed cortical shifts in the faceresponsiveloci of the ventral processing stream (VPS), an inferior occipito-temporalregion known to function in higher visual processing. Older children and adults recruitedmore anterior regions of the ventral processing stream than younger children. Toinvestigate the potential cognitive basis for these developmental changes, researchersimplemented a shape-matching task with parametric variations of shape overlap,structural similarity (SS), in stimulus pairs. VPS regions sensitive to high SS emerged inolder children and adults. Younger children recruited no structurally-sensitive regions inthe VPS. Two right hemisphere VPS regions were sensitive to maturational changes inSS. A comparison of face-responsive regions from the passive viewing task and the VPSSS regions did not reveal overlap. Though SS drives organization of the VPS, it did notexplain the cortical shifts in the neural substrates for face processing. In addition to VPSregions, results indicated additional maturational SS changes in frontal, parietal, andcerebellar regions. Based on these findings, further analyses were conducted to quantifyand qualify maturational changes in face and object processing throughout the brain.Results indicated developmental changes in activation extent, signal magnitude, andlateralization of face and object recognition networks. Collectively, this project supportsa developmental change in visual processing between 5-8 years and 9-11 years of age.Chapters Four through Six provide an in-depth discussion of the implications of thesefindings.

Prior research shows that stylistic ad manipulations (i.e., the style or manner in which product visuals are presented in an ad) impact consumer perceptions (Yang, Zhang and Peracchio 2010). This dissertation explores the impact of presence (versus absence) of a product’s shadow in the ad frame, as a visual stylistic manipulation influencing consumer ad perceptions. While many stylistic manipulations have been explored in the past, product shadows in how they impact ad perceptions have not been explored. Drawing on a holistic understanding on object shadows from the visual art, cognition and psychophysics literature streams, this dissertation investigates how product shadows impact ad perceptions. It applies theoretical tenants of Gestalt psychology, Construal Level Theory (CLT), and information paradigms including Signal Detection Theory (SDT) in deriving seven specific hypotheses. It also tests for moderating factors (such as individual consumer aesthetics, gestalt versus component visual processing modes, and product luxury positioning) that may alter consumer ad evaluations and ad effectiveness perceptions based on this stylistic manipulation of product shadow. Findings from this dissertation reveal that the presence (vs. absence) of a product’s shadow in an ad frame enhances the product’s visual form. This visual appraisal of the product in the ad frame further improves the ad’s overall evaluations. The effects of a product shadow on ad attitudes is positively moderated by an individual’s aesthetic tendencies (specifically their response tendencies towards visual aesthetics), a gestalt-focused (vs. component-focused) visual processing mode, as well as a luxury based ad’s positioning. There is also some support for negative effects of product shadows in component-focused ad scenarios, where they act as visual impairments rather than enhancers of the product form and aesthetics. Theoretically, this dissertation extends prior research on stylistic manipulations of product images in visual ad frames, while building upon established ad communication paradigms, including AIDA and Hierarchical Processing Model, HPM (Peracchio and Meyers-Levy 2005; Yang, Zhang and Peracchio 2010). Managerially, findings from this dissertation have implications for print, online, in-store and thus, any form of visual advertising portraying a product form. It outlines specific contexts under which managers can systematically employ (or evade) product shadows to not only enhance ad evaluations, but also to optimize their ad message efficacies. Stylistic image manipulations comprise production elements (e.g., camera angles), and only affect the way in which the product is displayed, i.e., not the core product image itself (Peracchio and Meyers-Levy 2005; Yang, Zhang and Peracchio 2010). Hence, these can be employed as strategic tools towards ad effectiveness (Barry and Howard 1990). Marketers can not only specifically target and position promotions incorporating product shadows towards aesthetically-attuned consumers, but also save advertising costs by omitting them if their presence hinders the communication of the intended message in certain scenarios.

Psychostimulants are known to alter visual function acutely and on withdrawal, and can cause attention deficit following prenatal exposure. However, psychostimulants can also improve visual attention in patients with attention deficit. The mechanisms involved in these contrasting effects remain largely unknown. To determine the role of specific brain regions and the dopamine system in the impact of cocaine exposure on visual processing, we employed two-photon microscopy and a transgenic larval zebrafish expressing the calcium indicator GCaMP-HS. We documented neuronal responses to contrasting visual stimuli, red light (LF) and dark (DF) flashes. We found that in the optic tectum neuropil (TOn), both stimuli elicited similar responses, though after repeated stimulus presentation, habituation developed to dark flash only. The dorsal telencephalon (dTe) responded and habituated to LF only. Acute cocaine (0.5 μM) reduced neuronal responses to LF in both brain regions and prevented habituation of dTe neurons to LF, but did not modify responses or habituation to dark flash. Prenatal cocaine exposure (PCE) did not modify baseline responses, but it prevented the acute effects of cocaine on LF responses in both regions and habituation in dTe, with no impact on dark flash responses. PCE also significantly reduced D1 dopamine receptor expression in TOn and cerebellum, but not dTe or the eye. Fish lacking the dopamine transporter (DATKO) retained normal D1 expression throughout the brain, baseline responses to LF in both TOn and dTe, and response reduction following cocaine in TOn. However, they demonstrated abnormal swimming behavior, and neither their swimming behavior nor dTe responses to LF were modified by cocaine. We discovered that in zebrafish, a diurnal vertebrate, responses to light not only require the primary visual processing center TO (superior colliculus in mammals), but also higher level processing by dTe. Responses to light but not darkness are modified by cocaine, unless the fish lack DAT or were exposed to PCE. Together, our results demonstrate specific effects of cocaine on visual processing mediated by the dopamine system, and provide a novel animal model for further investigation of these phenomena and development of new therapeutic approaches.

No description available.

Sensory overload is the feeling of over-stimulation that may lead to increased anxiety and panic in individuals with psychiatric disorders such as autism, post traumatic stress disorder, etc. Understanding visual processing is crucial to enhancing our treatments for disorders where sensory overload is a symptom. How do changes in internal states such as stress or hunger alter visual processing? This project aims to explore how visual processing is affected by signaling in the hypothalamus, an area of the brain regulating changes in internal states and stress. Preliminary studies revealed there are a number of neurons projecting from the lateral area of the hypothalamus to the visual cortex. We want to understand the specific location, identity, and neural circuits of these neurons. Visual cortex neurons were retrogradely traced to identify which inputs originate from the hypothalamus, and the geographical location of these cells was mapped out. The molecular identities of these projection neurons was further explored using specific RNAScope probes to check if those cells are expressing any of four genes most commonly expressed in the hypothalamus: Gal, Crh, Hcrt, and Pmch. This exploration will help us understand the type of signals communicated from the hypothalamic nuclei to the visual cortex to modulate visual processing.