Marisa Carrasco - US grants

Dr. Marisa Carrasco-Queijeiro began her five-year NYI award at Wesleyan University in FY 1993. The abstract is under the original award # SBR-9357986. Dr. Carrasco-Queijeiro has moved to New York University, and will finish the last three years of her award there. The original abstract is still valid.

Attention allows us to select and grant priority in processing to certain location or objects in the environment. Does attention affect the appearance of objects? This question was central for the founders of experimental psychology and psychophysics. At the end of the XIX century and at the beginning of the XX century, Wundt, James, Titchener and Mach, among others, proposed that attention intensifies the sensory impression, whereas others, like Fechner, denied such an idea. This is still a critical issue in perception and cognition. Most researchers believe that attention affects perception. However, there is a long-standing debate about how and when this comes about. A central goal of current psychophysical and neurophysiological studies of attention is to determine the level of processing at which attention starts modulating visual cognition and to characterize how that modulation takes place. My students and I have reported attentional effects on basic, early visual tasks that had previously been considered to be performed preattentively; e.g., visual search for features, orientation discrimination threshold, texture segmentation, and spatial resolution tasks. Moreover, we have shown that covert attention increases spatial resolution at the attended location. We will further explore the mechanisms underlying visual attention and will investigate the way they affect early visual processes. We will concentrate on characterizing two (not mutually exclusive) mechanisms proposed to underlie the processes by which attention affects perceptual performance, namely, signal enhancement and external noise reduction. 1) We will examine the extent to which contrast sensitivity is affected by covert attention. In particular, to assess whether covert attention affects the contrast sensitivity function (CSF) by increasing contrast gain or by shifting the tuning of the spatial filters, we will investigate if there isan interaction between target eccentricity and degree of attentional effect for different spatial frequencies. In addition, we will evaluate whether the performance fields are determined by visual or attentional variables. 2) We will investigate how the presence of homogeneous or heterogeneous distractors affects contrast sensitivity in orientation discrimination, detection and localization tasks. These manipulations will allow us to study the interaction of signal enhancement and external noise reduction. 3) By using a texture segmentation task that we have used previously, we will be able to ask more refined questions regarding the resolution hypotheses as well as the levels of processing at which the attentional mechanisms exert their effect. We will determine whether the attentional effect is driven by first- or second-order filters and if the attentional effects in texture segmentation differ in the upper and lower visual fields. Lastly, we will use the procedure of selective adaptation to learn more about the interaction between visual and attentional variables underlying performance in this segmentation task.

[unreadable] DESCRIPTION (provided by applicant): How does attention affect perception? The long-term objective of the research is to contribute to the understanding of visual attention by studying the effects of covert attention on early vision, drawing on theoretical work in perception, cognition, and neurophysiology, and using methods from visual psychophysics. There are two systems of covert attention: 'transient' (exogenous or stimulus-driven) and 'sustained' (endogenous or conceptually-driven). Recent research has shown that transient attention affects early vision by enhancing contrast sensitivity, increasing spatial resolution, and accelerating information accrual. To date, studies on sustained attention have focused on higher cognitive processes, whereas relatively little is known about its effects on early vision. The proposed research will systematically investigate the effects of both attentional systems on early vision. Research has shown that transient attention, being automatic, may result in impaired performance or deviate us from veridical perception. A main objective of the current proposal is to test the hypothesis that sustained attention is more flexible and hence may adapt to task demands better than transient attention. The specific aims are to investigate: (1) the effects of transient and sustained attention on contrast sensitivity by evaluating the quality of the signal at both the attended and unattended locations across the visual field, examining the time course of attentional effects on contrast sensitivity, and exploring how the gain mechanisms of attention and selective adaptation affect stimulus processing; (2) the effects of transient and sustained attention on spatial resolution at the attended and unattended locations and whether attention affects the channels' spatial frequency tuning by increasing sensitivity to higher frequencies; (3) whether transient and sustained attention differentially affect the gain and tuning of 1st and 2nd order spatial frequency channels; (4) the levels at which transient and sustained attention exert their effects on contrast sensitivity and spatial resolution by studying binocular rivalry; (5) the effects of covert attention on apparent contrast and spatial resolution during standard binocular viewing and binocular rivalry. Results will be interpreted within the theoretical framework of an ensemble of spatial filters operating in linear and nonlinear regimes. The findings have implications for human factors, as well as for our understanding of many neuropsychological conditions, e.g. unilateral neglect, schizophrenia, and ADHD. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Attention and perceptual learning (PL) are two mechanisms known to improve visual perception, though, for the most part, they have been studied separately. I propose to thoroughly investigate the effects of manipulating covert attention on PL. PL involves relatively long-lasting (weeks or months) changes to an organism's perceptual system. Such changes improve the ability to respond to events in the environment and are considered a manifestation of neural plasticity in the adult brain. PL has been demonstrated psychophysically for many stimuli in various sensory modalities, and is often highly specific to stimulus and task. For instance, if observers learn (in the initial training phase) how to perform a task at a particular location in the visual field, they later (in the testing phase) show no benefit at untrained locations. Attention operates on a much shorter timescale than PL and is the most important mechanism that selectively and dynamically improves perceptual performance. Covert attention - the selective processing of information at a given location without eye movements to that location - improves perceptual performance on many detection, discrimination and localization tasks in early vision. I am interested in how exogenous (involuntary) and endogenous (voluntary) covert attention affect the hallmark specificity of PL, and whether attention can interact with learning to overcome this limitation to the improvement in performance PL engenders. I will use visual dimensions for which both PL specificity and modulation by attention have been shown;e.g., location, orientation and spatial frequency. Investigating the psychophysical changes associated with the effects of attention on PL will lead to increased understanding of plasticity in the visual system. The question of whether and how different forms of attention enhance plasticity in the adult cortex is important theoretically and has practical consequences. PL probably underlies most of what we do well visually in our professional and personal lives and is thus of enormous basic interest and practical importance. This question is also crucial for understanding and evaluating the potential of rehabilitation following damage to the visual system. Our own studies on the effects of attention on early vision conducted during the period of the current grant place us in a unique position to conduct the proposed research. Pilot studies indicate that attention plays a pivotal and unanticipated role in PL. I will characterize the effects of each type of attention, endogenous and exogenous, for the following aims: (1) PL in visual search across the visual field;(2) PL of basic dimensions (e.g., contrast sensitivity, orientation and spatial resolution) with regard to location specificity, taking into account retinal distance, cortical distance and the size of the attentional window;(3) PL with regard to feature (e.g., contrast sensitivity, orientation) learning and transfer specificity;(4) PL in the absence of awareness. The proposed research will utilize different psychophysical procedures to contribute to our understanding of how brain plasticity alters vision as indicated by PL, and how visual processing interacts with other brain systems underlying cognition, in particular, attention. The findings will have theoretical relevance and will contribute to our understanding and evaluation of potential of rehabilitation following damage to the visual system. PUBLIC HEALTH RELEVANCE: I propose to thoroughly investigate the effects of manipulating covert attention on PL. PL is the foundation of our visual competence, so the question of whether and how different forms of attention may enhance plasticity in the adult cortex in the general population is important theoretically and has practical consequences. The experimental protocols that I will develop for studying how attention affects perceptual learning in healthy human observers will be readily applicable to patient populations. A better understanding of visual attention and perceptual learning with healthy observers will lead to a better understanding of factors limiting peripheral vision, which are critical when central vision is compromised due to macular degeneration and related visual deficits. Basic knowledge of visual attention has implications for our understanding of several neuropsychological disorders and for informing the development of their diagnostic testing, including unilateral neglect, schizophrenia and ADHD. Basic knowledge of how attention affects perceptual learning has implications for rehabilitation of patients with amblyopia, macular degeneration, and cortical blindness as well as for the evaluation of the potential of visual rehabilitation after trauma and tumors or infarcts ('stroke').

DESCRIPTION (provided by applicant): Attention has played a central role in perception research since the dawn of experimental psychology. Over the past 20 years, the neurophysiological basis of visual attention has become an active area of research, and the field of visual psychophysics has developed rigorous methods for measuring and characterizing the effects of attention on visual performance, yielding an explosion of findings. These experiments have documented a bewildering variety of empirical phenomena, some of which appear to be mutually contradictory. One example concerns the interaction between attention and visual stimulus contrast. The results of some experiments suggest that attention increases neuronal responses multiplicatively by applying a fixed response gain factor. Other results suggest a change in contrast gain. Still other results suggest that attention may have a fixed additive effect, which can be approximated as a combination of both response gain and contrast gain changes. These ostensibly contradictory empirical findings have been paralleled by theoretical ideas that have been taken to represent alternative models of attention. We propose to develop and test a computational theory, called the normalization model of attention, and to unify/reconcile various alternative, and seemingly conflicting, empirical findings and theoretical models of the effects of attention on neuronal activity in visual cortex. We aim: (1) to show that the proposed model can exhibit response gain changes, contrast gain changes, and additive-like combinations of response and contrast gain changes, depending on the stimulus conditions and the spread of the attention field;(2) to test the hypothesis that the effect of attention on behavioral performance and perceptual appearance systematically shifts from a change in response gain to contrast gain by manipulating the stimulus size and the spatial extent of the attention field;and (3) to test the hypothesis that attention modulates activity in visual cortex as predicted by the model, and to link attentional modulation of cortical activity (as measured with functional magnetic resonance imaging) with attentional modulation of behavioral performance (as measured psychophysically). The proposed research will utilize convergent information gained from various techniques (computational theory, previous electrophysiology experiments, and novel psychophysics and functional imaging experiments) to contribute to our understanding of how the brain processes visual information, how neural activity is related to visual attention and perception, and how visual processing interacts with other brain systems underlying cognition, in particular, attention. PUBLIC HEALTH RELEVANCE: The experimental protocols and theoretical principles that we develop for studying vision and attention in healthy human subjects will be readily applicable to patient populations. A better understanding of visual attention will lead to a better understanding of factors limiting peripheral vision, which are critical when central vision is compromised due to macular degeneration and related visual deficits. Basic knowledge of visual attention has implications for our understanding of several neuropsychological disorders, including unilateral neglect, schizophrenia and ADHD, and for informing the development of diagnostic tests of these disorders.

Periodic fluctuations of neuronal activity, i.e. oscillations, have a functional role in visual perception, which is improved by covert attention (our ability to selectively process information at one location in the visual scene without eye movements). Oscillatory brain activity correlates with the engagement of visuospatial attention and influences performance in healthy observers. In neurological patients, abnormal oscillatory activity following brain damage accompanies visual impairments. However, no study has systematically manipulated either cor- tical oscillatory activity, or its interaction with covert attention, to improve visual performance in healthy adults, using Transcranial Magnetic Stimulation (TMS); a well-established, focal and non-invasive brain stimulation technique. This knowledge is important to improve perceptual function in healthy human observers and rehabil- itate faulty perception in patients. With healthy observers, we will use TMS rhythmic patterns to entrain local oscillatory activity in specific cortical sites alone and/or in combination with attention. We will assess whether the entrainment of oscillatory activity (i.e., phase alignment and increased power) facilitates contrast sensitivi- ty?a fundamental, well-understood visual dimension determining the window of visibility, which is increased by attention. In Aim 1, we will test the ability of oscillation-tailored rhythmic TMS to improve visual performance, and record its time-frequency signature. We will apply either brief rhythmic active TMS or rhythmic sham (non- magnetic placebo) stimulation at the Alpha?10Hz and Beta?30Hz frequencies, at stimulus onset to two cortical areas involved in the modulation of perception and attention: right occipital (V1) and frontal (FEF) sites. We explore the effect of phase by manipulating the interval between display and TMS burst onsets. While manipu- lating phase, we will compare the impact of (a) rhythmic active vs. random active TMS (same pulse number and duration); (b) rhythmic sham vs. random sham stimulation; (c) rhythmic active TMS vs. rhythmic sham sti- mulation; (d) random active TMS vs. random sham stimulation, on threshold and asymptotic performance to assess changes in contrast gain and/or response gain. In Aim 2, we will concentrate on the most effective cor- tical site-frequency-phase pattern combination found in Aim 1, as assessed by the size of the effects and con- sistency across observers, to test whether covert attention can potentiate such effects. We will manipulate ex- ogenous (involuntary, reflexive) attention, which is not cognitively demanding and has been well-characterized with psychophysics, neuroimaging and electrophysiology. By conducting concurrent TMS-EEG recordings while observers perform a discrimination task, we will increase our understanding of how the brain processes visual information, how the entrainment of neural activity is related to perceptual improvements, and how cov- ert attention affects spatial and temporal aspects of visual processing. In addition, this proposal will probe the feasibility of non-invasive neurostimulation combined with attentional manipulations to entrain brain oscillatory activity and improve visual function in healthy observers, and, in the future, restore vision in patients.

Project Summary The long-term objective is to understand how visual performance varies across the visual field during childhood, adolescence and adulthood, and the neural correlates and possible oculomotor correlates underlying such changes. Vision at the center of gaze (fovea) has high sensitivity and resolution, facilitating good performance in many tasks, but performance decreases with increasing distance from fovea. Simple radial distance from fovea ?eccentricity? is not the only relevant retinotopic parameter for perception. At any given eccentricity stimuli can fall anywhere along circle, and the polar angle of a stimulus at ?isoeccentric? locations also has pronounced effects on perception in human adults, captured by a Performance Fields (PF) map. And yet the role of the polar angle has not been studied in children and adolescents, and the underlying neural representations and possible oculomotor correlates are practically unknown. PF present an opportunity for establishing tight quantitative links between behavior and neural representations of visual space. The proposed studies will measure PF in children, adolescents and adults, under different attentional states (Aim 1), along with fMRI visual field maps (Aim 2) and fixational oculomotor behavior (Aim 3). By highlighting and characterizing the functional, oculomotor and neural correlates of PF and their modulations across multiple timescales, the proposed studies will elucidate critical constraints on perception and performance as a function of polar angle. We will implement a computational observer model that is the glue that binds the three aims together. In addition to advancing our knowledge of visual perception, the proposed research will enable us to make predictions about human performance. The characterization of PF has significant implications for ergonomic and human factors applications, which should take into account functional plasticity during development, compensation via selective attention, and oculomotor behavior. For example, it is of critical importance for user-interfaces that present information at different locations of the visual field. With an understanding of how attention affects PF we can extend our knowledge to real-world displays, such as navigation and cockpit alerting systems, control panel layouts in cars, computer-aided detection systems, and software for presenting radiological images. Furthermore, the gained knowledge can aid the design of artificial image recognition systems. This research will inform the development of compensatory strategies and interventions to deal more effectively with the limitations of the visual system. In addition, understanding the functional causes of performance differences across the visual field and how attention and/or oculomotor behavior interact with them will improve our models of visual dysfunction (e.g., macular degeneration, retinitis pigmentosa), as well as the diagnosis of these disorders.

Project Summary Visual information entering the brain is constantly changing. Its interpretation depends on the observers' goals, and on cognitive states that also change in response to current and previous input. Yet most of our knowledge of vision deals with spatial vision and spatial attention, and most existing computational models of vision and visual attention are static; they deal with stimuli that are isolated in time. This represents a critical barrier to a comprehensive theory of visual perception and attention. Temporal attention is the prioritized processing of a stimulus at a specific point in time, which can be voluntary, when a stimulus time can be anticipated, or invol- untary, when attention is triggered automatically by a stimulus. The impact of temporal attention on perception and sensory cortical responses has been little investigated, despite its indispensable role in our understanding of a constantly changing environment. We propose to fill this critical gap in the cognitive neuroscience of at- tention. Our long-term goal is to develop a spatiotemporal theory of cortical computation, widely applicable in basic and translational research in perceptual and cognitive neuroscience. Our short-term goal is to investi- gate temporal attention to understand how perception is shaped by dynamic interactions between sensory in- put and attentional modulation, and how visual cortical processing underlies those interactions. We propose an innovative theoretical framework, which makes explicit how perception and attention interact across time (Aim 1). Two alternative dynamic models, early-gain vs. late-competition, in which temporal at- tention modulates different stages of processing, will be tested and constrained with data gathered with innovative experimental protocols, combining behavioral (psychophysics; Aim 2) and neuroimaging (magne- toencephalography, MEG; Aim 3) methods. Because orientation processing is well-characterized psychophysi- cally and neurophysiologically in a static setting, we will use orientation discrimination and estimation tasks to determine the dynamic interactions between perception and attention. The empirical results will significantly advance our understanding of the time-course, perceptual consequences, resource limitations, and underlying neural mechanisms of temporal attention, and will also distinguish between alternative models and constrain model parameters. By integrating theory with behavioral and neuroimaging data, we will characterize how tem- poral attention dynamically changes perception and neural responses. The proposed research is fully in line with the NEI mission. It investigates how temporal attention modulates brain processing of visual information and how neural activity relates to visual perception. Further, because dynamic attention allocation is a central function of the visual system, the proposed research in healthy observ- ers will be readily applicable to translational research in special populations, and may advance our understand- ing of abnormalities in temporal processing and temporal attention that have been associated with personality traits, like impulsivity, and prevalent disorders such as ADHD, autism, visual neglect and dyslexia.

Abstract The Functional Imaging Module supports vision research in the Center for Brain Imaging at New York University. CBI is a shared research center for research and teaching in visual and cognitive neuroscience at NYU. CBI is located on the ground and second floors of the same building that houses most of the vision core faculty, and houses facilities for MRI, MEG, EEG, and TMS. The CBI is now in its sixteenth full year of operation, and members of the Core faculty are among its most active users. The Functional Imaging Module will enable NEI grantees and other vision researchers to develop, implement, and maintain technical advances, to benefit from specialized tools developed and used by individual labs, to use and contribute to a database of human research subjects with extensive vision-related brain and behavioral measures, to standardize and improve image processing pipelines, to support MRI-compatible TMS, to facilitate the public sharing of data, to develop shared software for acquisition and processing of monkey MRI data (structural, diffusion, and functional), and to develop software to integrate data acquired through the multiple measurement modalities available at the Center for Brain Imaging. The module will leverage research support by stimulating collaborative research between members of the Core faculty, and by facilitating sharing techniques and instrumentation between members of the Core faculty. If requested, the technical developments will also be shared with vision scientists at other institutions. The Functional Imaging Module provides moderate or extensive support for 16 members of the Vision Core, including two young investigators and 10 NEI funded investigators who hold qualifying grants.