Locomotion through the environment and interactions with objects depend on fundamental processes of surface segmentation. This project will study the neural mechanisms that support surface segmentation using a combination of functional Magnetic Resonance (fMRI), electro- electroencephalographic (EEG) and magneto-encephalographic (MEG) imaging studies. Elementary encephalographic aspects of surface segmentation will be studied with reduced cue stimuli that control the availability of temporal frequency, orientation, phase and direction cues as inputs to the figure/ground segmentation process. Cortical areas involved in form and motion-based segmentation will be localized functionally using both fMRI and electromagnetic source estimation techniques. The spatial relationship of this functional activation to visual areas defined by retinotopic mapping will also be determined. These studies will determine how the different segmentation cues are combined in different cortical areas and at different times after stimulus onset. A further goal of the imaging experiments is to determine whether border information is extracted prior to surface information or vice versa. To better understand the neural computations involved in segmentation we will apply a non-linear analysis technique based on binary m-sequences to study the time-evolution of segmentation-related activity recorded from the EEG and MEG. The technique measures time evolution of the strength and sign of interaction (facilitation or suppression) between figure and background as a function of their spatio- spatiotemporal configuration. The technique also yields a functional model of the evoked response that can temporal predict responses to the simpler stimuli that will be used in the imaging experiments. The validity of the model will be tested by comparing model predictions for simple stimuli to those actually measured. Finally, we will examine segmentation performance in strabismus patients with a history of abnormal visual experience during early development that leads to defective or absent stereopsis and nasalward/temporal biases in motion processing. Results from the current project period suggest that these patients will have deficits on figure/ground segmentation that are independent of acuity deficits. This study will also determine whether nasalward/temporal biases previously reported for large field uniform stimuli propagate to the figure/ground segmentation process.
| Tsai, Jeffrey J; Norcia, Anthony M; Ales, Justin M et al. (2011) Contrast gain control abnormalities in idiopathic generalized epilepsy. Ann Neurol 70:574-82 |
| Baker, Thomas J; Norcia, Anthony M; Candy, T Rowan (2011) Orientation tuning in the visual cortex of 3-month-old human infants. Vision Res 51:470-8 |
| Appelbaum, L G; Ales, J M; Cottereau, B et al. (2010) Configural specificity of the lateral occipital cortex. Neuropsychologia 48:3323-8 |
| Palomares, Melanie; Pettet, Mark; Vildavski, Vladimir et al. (2010) Connecting the dots: how local structure affects global integration in infants. J Cogn Neurosci 22:1557-69 |
| Ales, Justin M; Yates, Jacob L; Norcia, Anthony M (2010) V1 is not uniquely identified by polarity reversals of responses to upper and lower visual field stimuli. Neuroimage 52:1401-9 |
| Appelbaum, Lawrence G; Wade, Alex R; Pettet, Mark W et al. (2008) Figure-ground interaction in the human visual cortex. J Vis 8:8.1-19 |
| Pei, Francesca; Pettet, Mark W; Norcia, Anthony M (2007) Sensitivity and configuration-specificity of orientation-defined texture processing in infants and adults. Vision Res 47:338-48 |
| Appelbaum, L Gregory; Wade, Alex R; Vildavski, Vladimir Y et al. (2006) Cue-invariant networks for figure and background processing in human visual cortex. J Neurosci 26:11695-708 |
| Candy, T R; Skoczenski, A M; Norcia, A M (2001) Normalization models applied to orientation masking in the human infant. J Neurosci 21:4530-41 |
| Brown, R J; Candy, T R; Norcia, A M (1999) Development of rivalry and dichoptic masking in human infants. Invest Ophthalmol Vis Sci 40:3324-33 |
