15 research outputs found
On the effectiveness of noise masks: Naturalistic vs. un-naturalistic image statistics
AbstractIt has been argued that the human visual system is optimized for identification of broadband objects embedded in stimuli possessing orientation averaged power spectra fall-offs that obey the 1/fβ relationship typically observed in natural scene imagery (i.e., β=2.0 on logarithmic axes). Here, we were interested in whether individual spatial channels leading to recognition are functionally optimized for narrowband targets when masked by noise possessing naturalistic image statistics (β=2.0). The current study therefore explores the impact of variable β noise masks on the identification of narrowband target stimuli ranging in spatial complexity, while simultaneously controlling for physical or perceived differences between the masks. The results show that β=2.0 noise masks produce the largest identification thresholds regardless of target complexity, and thus do not seem to yield functionally optimized channel processing. The differential masking effects are discussed in the context of contrast gain control
The what and why of perceptual asymmetries in the visual domain
Perceptual asymmetry is one of the most important characteristics of our visual
functioning. We carefully reviewed the scientific literature in order to examine
such asymmetries, separating them into two major categories: within-visual field
asymmetries and between-visual field asymmetries. We explain these asymmetries
in terms of perceptual aspects or tasks, the what of the
asymmetries; and in terms of underlying mechanisms, the why of
the asymmetries. Tthe within-visual field asymmetries are fundamental to
orientation, motion direction, and spatial frequency processing. between-visual
field asymmetries have been reported for a wide range of perceptual phenomena.
foveal dominance over the periphery, in particular, has been prominent for
visual acuity, contrast sensitivity, and colour discrimination. Tthis also holds
true for object or face recognition and reading performance. upper-lower visual
field asymmetries in favour of the lower have been demonstrated for temporal and
contrast sensitivities, visual acuity, spatial resolution, orientation, hue and
motion processing. Iin contrast, the upper field advantages have been seen in
visual search, apparent size, and object recognition tasks. left-right visual
field asymmetries include the left field dominance in spatial (e.g.,
orientation) processing and the right field dominance in non-spatial (e.g.,
temporal) processing. left field is also better at low spatial frequency or
global and coordinate spatial processing, whereas the right field is better at
high spatial frequency or local and categorical spatial processing. All these
asymmetries have inborn neural/physiological origins, the primary
why, but can be also susceptible to visual experience, the
critical why (promotes or blocks the asymmetries by
altering neural functions)
fMRI reveals a lower visual field preference for hand actions in human superior parieto-occipital cortex (SPOC) and precuneus
Humans are more efficient when performing actions towards objects presented in the lower visual field (VF) than in the upper VF. The present study used slow event-related functional magnetic resonance imaging (fMRI) to examine whether human brain areas implicated in action would show such VF preferences. Participants were asked to fixate one of four different positions allowing objects to be presented in the upper left, upper right, lower left or lower right VF. In some trials they reached to grasp the object with the right hand while in others they passively viewed the object. Crucially, by manipulating the fixation position, rather than the position of the objects, the biomechanics of the movements did not differ across conditions. The superior parieto-occipital cortex (SPOC) and the left precuneus, brain areas implicated in the control of reaching, were significantly more activated when participants grasped objects presented in the lower VF relative to the upper VF. Importantly, no such VF preferences were observed in these regions during passive viewing. This finding fits well with evidence from the macaque neurophysiology that neurons within visuomotor regions over-represent the lower VF relative to the upper VF and indicate that the neural responses within these regions may reflect a functional lower VF advantage during visually-guided actions