Clinical Research Directory

Probing the Role of Feature Dimension Maps in Visual Cognition: Manipulations of Relevant Locations on Salience Processing? (Expt 3.1 Pilot)

How do we know what's important to look at in the environment? Sometimes, we need to look at objects because they are 'salient' (for example, bright flashing lights of a police car, or the stripes of a venomous animal), while other times, we need to ignore irrelevant salient locations and focus only on locations we know to be 'relevant'. These behaviors are often explained by the use of 'priority maps' which index the relative importance of different locations in the visual environment based on both their salience and relevance. In this research, we aim to understand how these factors interact when determining what's important to look at. Specifically, we are evaluating the extent to which the visual system considers locations that are known to be irrelevant when considering the salience of objects. We're testing the hypothesis that the visual system always computes maps of salient locations within 'feature maps', but that activity from these maps is not read out to guide behavior for task-irrelevant locations. We'll have people look at displays containing colored shapes and/or moving dots and report aspects of the visual stimulus (e.g., orientation of a line within a particular stimulus). We'll measure response times across conditions in which we manipulate the presence/absence of salient distracting stimuli and provide various kinds of cues about the potential relevance of different locations on the screen. The rationale is that by measuring changes in visual search behavior (and thus inferring computations performed on brain representations), we will determine how these aspects of simplified visual environments impact the brain's representation of important object locations. This will support future studies using brain imaging techniques aimed at identifying the neural mechanisms supporting the extraction of salient and relevant locations from visual scenes, which can inform future diagnosis/treatment of disorders which can impact our ability to perform visual search (e.g., schizophrenia, Alzheimer's disease).

Probing the Role of Feature Dimension Maps in Visual Cognition: Impact of Task Demands (Expt 2.1)

How does one know what to look at in a scene? Imagine a "Where's Waldo" game - it's challenging to find Waldo because there are many 'salient' locations in the picture, each vying for one's attention. One can only attend to a small location on the picture at a given moment, so to find Waldo, one needs to direct their attention to different locations. One prominent theory about how one accomplishes this claims that important locations are identified based on distinct feature types (for example, motion or color), with locations most unique compared to the background most likely to be attended. An important component of this theory is that individual feature dimensions (again, color or motion) are computed within their own 'feature maps', which are thought to be implemented in specific brain regions. However, whether and how specific brain regions contribute to these feature maps remains unknown. The goal of this study is to determine how brain regions that respond strongly to different feature types (color and motion) and which encode spatial locations of visual stimuli transform 'feature dimension maps' based on stimulus properties as a function of task instructions. The investigators hypothesize that feature-selective brain regions act as neural feature dimension maps, and thus encode representations of relevant location(s) based on their preferred feature dimension, such that the stimulus representation in the most relevant feature map is up-regulated to support adaptive behavior. The investigators will scan healthy human participants using functional MRI (fMRI) in a repeated-measures design while they view visual stimuli made relevant based on a cued feature dimension (e.g., color or motion). The investigators will employ state-of-the-art multivariate analysis techniques that allow them to reconstruct an 'image' of the stimulus representation encoded by each brain region to dissect how neural tissue identifies salient locations. Each participant will perform a challenging discrimination task based on the cued feature (report motion direction or color of stimulus dots) of a stimulus presented in the periphery, which are identical across trial types. Across trials the investigators will manipulate the attended feature value (color, motion, or fixation point). This manipulation will help the investigators fully understand these critical relevance computations in the healthy human visual system.