Visual Performance Fields: Frames of Reference

Performance in most visual discrimination tasks is better along the horizontal than the vertical meridian (Horizontal-Vertical Anisotropy, HVA), and along the lower than the upper vertical meridian (Vertical Meridian Asymmetry, VMA), with intermediate performance at intercardinal locations. As these inhomogeneities are prevalent throughout visual tasks, it is important to understand the perceptual consequences of dissociating spatial reference frames. In all studies of performance fields so far, allocentric environmental references and egocentric observer reference frames were aligned. Here we quantified the effects of manipulating head-centric and retinotopic coordinates on the shape of visual performance fields. When observers viewed briefly presented radial arrays of Gabors and discriminated the tilt of a target relative to homogeneously oriented distractors, performance fields shifted with head tilt (Experiment 1), and fixation (Experiment 2). These results show that performance fields shift in-line with egocentric referents, corresponding to the retinal location of the stimulus

In pursuit of delay-related brain activity for anticipatory eye movements

How the brain stores motion information and subsequently uses it to follow a moving target is largely unknown. This is mainly due to previous fMRI studies using paradigms in which the eye movements cannot be segregated from the storage of this motion information. To avoid this problem we used a novel paradigm designed in our lab in which we interlaced a delay (2, 4 or 6 seconds) between the 1st and 2nd presentation of a moving stimulus. Using this design we could examine brain activity during a delay period using fMRI and have subsequently found a number of brain areas that reveal sustained activity during predictive pursuit. These areas include, the V5 complex and superior parietal lobe. This study provides new evidence for the network involved in the storage of visual information to generate early motor responses in pursuit

Mineral Components and Ash Analysis

RESP-3539

Altered visuo-spatial processing in the peri-personal space: a new look at the hand-proximity effects

The previous studies have shown the importance of body in the visuo-spatial representation of space and the objects in it. Perception of objects located near the body trigger activations in brain regions involved in making voluntary movements. Such activations are restricted to the peripersonal space (PPS) particularly within a certain distance of the hand and are considered the visual receptive field of this space. Behavioral findings have shown reduced response time and enhanced accuracy for targets presented in the peri-hand space, referred to as the peri-hand effect. There has been considerable debate about the nature of these effects with some researchers arguing that it is attentional and others arguing that it is perceptual. In the current review, we summarize research about the PPS with a special focus on the peri-hand space and changes to visuo-spatial processing associated with objects places in this space. We suggest that there is enough evidence in the literature pointing at independent and dissociable perceptual and attentional effects in the peri-hand space. We also highlight the differences in the spatial extent of these effects for perception and attention. We propose that future studies looking at the peri-hand effects should dissociate these effects to better understand the nature of visual processing occurring in the peri-hand space.by Tony Thomas and Meera Mary Sunn