Local versus global contrasts in texture segregation

Mean orientation discrimination based on proximal stimuli

Ensemble perception refers to the ability to accurately and rapidly perceive summary statistical representations of specific features from a group of similar objects. However, the specific type of representation involved in this perception within a three-dimensional (3-D) environment remains unclear. In the context of perspective viewing with stereopsis, distal stimuli can be projected onto the retina as different forms of proximal stimuli based on their distances, despite sharing similar properties, such as object size and spatial frequency. This study aimed to investigate the effects of distal and proximal stimuli on the perception of summary statistical information related to orientation. In our experiment, we presented multiple Gabor patches in a stereoscopic environment, allowing us to measure the discrimination threshold of the mean orientation. The object size and spatial frequency were fixed for all patches regardless of depth. However, the physical angular size and absolute spatial frequency covaried with the depth. The results revealed the threshold elevation with depth expansion, especially when the patches formed two clusters at near and far distances, leading to large variations in their retinotopic representations. This finding indicates a minor contribution of similarity of the distal stimuli. Subsequent experiments demonstrated that the variability in physical angular size of the patches significantly influenced the threshold elevation in contrast to that of binocular disparity and absolute spatial frequency. These findings highlight the critical role of physical angular size variability in perceiving mean orientations within the 3-D space.

Criteria interactions across visual attributes

Judgmental interference in dual tasks has been demonstrated in conditions where the detection or discrimination of different contrast increments applied to two stimuli presented simultaneously or in sequence. The present work demonstrates such interference for changes along two distinct visual features, namely contrast and orientation, when simultaneously applied to the same or to two distinct objects (Gabor-patches). The interference reveals itself in the use of quasi-equal decision criteria for both dimensions, in conflict with an optimal behavior requiring that criteria be proportional to the sensitivities for the distinct changes. The quasi-equality of the criteria assessed for contrast and orientation changes implies the equality of the internal noises characterizing the respective detection process, hence suggesting that they are limited at the decision level. Among the conceptual consequences of this limitation are the existence of a meta-attribute decisional dimension (tantamount to that of a "central executive system") and the questionable merits of probability summation over spatial channels. In addition, the data show a significant sensitivity drop in the dual- with respect to the single-task conditions, all the more so when the modulated features belong to two objects rather than to the same object. While the sensitivity drop in dual tasks is the standard trademark of distributed attention, it is argued that decisional interference is yet another aspect of it.

Information limit on the spatial integration of local orientation signals

Channel-based models of human spatial vision require that the output of spatial filters be pooled across space. This pooling yields global estimates of local feature attributes such as orientation that are useful in situations in which that attribute may be locally variable, as is the case for visual texture. The spatial characteristics of orientation summation are considered in the study. By assessing the effect of orientation variability on observers' ability to estimate the mean orientation of spatially unstructured textures, one can determine both the internal noise on each orientation sample and the number of samples being pooled. By a combination of fixing and covarying the size of textured regions and the number of elements constituting them, one can then assess the effects of the texture's size, density, and numerosity (the number of elements present) on the internal noise and the sampling density. Results indicate that internal noise shows a primary dependence on texture density but that, counterintuitively, subjects rely on a sample size approximately equal to a fixed power of the number of samples present, regardless of their spatial arrangement. Orientation pooling is entirely flexible with respect to the position of input features.