J Vision
-
In crowding, target perception deteriorates in the presence of flanking elements. Crowding is classically explained by low-level mechanisms such as pooling or feature substitution. ⋯ Here we show that pattern completion, another grouping cue that is important for crowding in foveal vision, is also important in peripheral vision. We also describe computer simulations that show how pattern completion, and crowding in general, can be partly explained by recurrent processing.
-
Spatial filtering models are currently a widely accepted mechanistic account of human lightness perception. Their popularity can be ascribed to two reasons: They correctly predict how human observers perceive a variety of lightness illusions, and the processing steps involved in the models bear an apparent resemblance with known physiological mechanisms at early stages of visual processing. Here, we tested the adequacy of these models by probing their response to stimuli that have been modified by adding narrowband noise. ⋯ We discuss the reasons for failure for each model individually, but we argue that the failure is indicative of the general inadequacy of this class of spatial filtering models. Given the present evidence we do not believe that spatial filtering models capture the mechanisms that are responsible for producing many of the lightness phenomena observed in human perception. Instead we think that our findings support the idea that low-level contributions to perceived lightness are primarily determined by the luminance contrast at surface boundaries.
-
We measured pupil size in adult human subjects while we manipulated both the luminance of the visual scene and the location of attention. We found that, with central fixation maintained, pupillary constrictions and dilations evoked by peripheral luminance increments and decrements are larger when spatial attention is covertly (i.e., with no eye movements) directed to the stimulus region versus when it is directed to the opposite hemifield. ⋯ This indicates that a sizable portion of this simple ocular behavior—often considered a subcortical "reflex"—in fact depends on cortical processing. Together, these features indicate that pupillometry is not only an index of retinal and brainstem function, but also an objective measure of complex constructs such as attention and its effects on sensory processing.
-
Prior research on bilateral-stream Rapid Serial Visual Presentation (RSVP) displays reveals that participants often perceive left visual field (LVF) targets significantly sooner than right visual field (RVF) targets (Matthews, Welch, Festa & Clement, 2013). The hastened perception of LVF targets occurs for temporal order judgments (TOJs) but not simultaneity judgments (SJs) on the same stimuli. This demonstrates task-specific neural events for time perception. Here, we investigated the extent to which task-specific neural events govern time discrimination by evaluating whether training differentially affects the precision of SJs and TOJs. ⋯ In principle, precision on SJs and TOJs could depend on a shared computation, namely, the difference between two arrival times. Despite this, our perceptual learning data suggest a dissociation between the neural events mediating SJ and TOJ precision even when stimulation remains identical across tasks. Meeting abstract presented at VSS 2015.
-
Dynamic environments often contain features that vary simultaneously as well as features that vary sequentially. In principle, the correspondingly distinct sensations of simultaneity and temporal order could arise from a single shared neural computation that involves differencing two arrival times. On the other hand, simultaneity judgments (SJs) and temporal order judgments (TOJs) have distinct informational requirements that could be optimized by distinct neural events. ⋯ Specifically, simply repositioning targets from the LVF to the RVF generated mean TOJ threshold increases (temporal precision reductions) between 39% and 57%, an effect size equivalent to approximately two LVF detectors for each RVF detector. Control experiments indicated that this LVF advantage reflected the temporal resolution of visual attention, rather than lower-level flicker discrimination or masking. These findings constitute additional evidence for an LVF advantage in time-sensitive attentional tasks and further contradict our subjective experience of homogenous temporal precision across the visual field.