Extra-foveal Processing of Object Semantics Guides Early Overt Attention During Visual Search

Eye-tracking studies using arrays of objects have demonstrated that some high-level processing of object semantics can occur in extra-foveal vision, but its role on the allocation of early overt attention is still unclear. This eye-tracking visual search study contributes novel findings by examining the role of object-to-object semantic relatedness and visual saliency on search responses and eye-movement behaviour across arrays of increasing size (3, 5, 7). Our data show that a critical object was looked at earlier and for longer when it was semantically unrelated than related to the other objects in the display, both when it was the search target (target-present trials) and when it was a target’s semantically related competitor (target-absent trials). Semantic relatedness effects manifested already during the very first fixation after array onset, were consistently found for increasing set sizes, and were independent of low-level visual saliency, which did not play any role. We conclude that object semantics can be extracted early in extra-foveal vision and capture overt attention from the very first fixation. These findings pose a challenge to models of visual attention which assume that overt attention is guided by the visual appearance of stimuli, rather than by their semantics

Preserved Extra-Foveal Processing of Object Semantics in Alzheimer’s Disease

Alzheimer’s disease (AD) patients underperform on a range of tasks requiring semantic processing, but it is unclear whether this impairment is due to a generalised loss of semantic knowledge or to issues in accessing and selecting such information from memory. The objective of this eye-tracking visual search study was to determine whether semantic expectancy mechanisms known to support object recognition in healthy adults are preserved in AD patients. Furthermore, as AD patients are often reported to be impaired in accessing information in extra-foveal vision, we investigated whether that was also the case in our study. Twenty AD patients and 20 age-matched controls searched for a target object among an array of distractors presented extra-foveally. The distractors were either semantically related or unrelated to the target (e.g., a car in an array with other vehicles or kitchen items). Results showed that semantically related objects were detected with more difficulty than semantically unrelated objects by both groups, but more markedly by the AD group. Participants looked earlier and for longer at the critical objects when these were semantically unrelated to the distractors. Our findings show that AD patients can process the semantics of objects and access it in extra-foveal vision. This suggests that their impairments in semantic processing may reflect difficulties in accessing semantic information rather than a generalised loss of semantic memory

Fixation-related Brain Potentials during Semantic Integration of Object–Scene Information

In vision science, a particularly controversial topic is whether and how quickly the semantic information about objects is available outside foveal vision. Here, we aimed at contributing to this debate by coregistering eye movements and EEG while participants viewed photographs of indoor scenes that contained a semantically consistent or inconsistent target object. Linear deconvolution modeling was used to analyze the ERPs evoked by scene onset as well as the fixation-related potentials (FRPs) elicited by the fixation on the target object (t) and by the preceding fixation (t − 1). Object–scene consistency did not influence the probability of immediate target fixation or the ERP evoked by scene onset, which suggests that object–scene semantics was not accessed immediately. However, during the subsequent scene exploration, inconsistent objects were prioritized over consistent objects in extrafoveal vision (i.e., looked at earlier) and were more effortful to process in foveal vision (i.e., looked at longer). In FRPs, we demonstrate a fixation-related N300/N400 effect, whereby inconsistent objects elicit a larger frontocentral negativity than consistent objects. In line with the behavioral findings, this effect was already seen in FRPs aligned to the pretarget fixation t − 1 and persisted throughout fixation t, indicating that the extraction of object semantics can already begin in extrafoveal vision. Taken together, the results emphasize the usefulness of combined EEG/eye movement recordings for understanding the mechanisms of object–scene integration during natural viewing

Qualitative patterns at Raven’s colored progressive matrices in mild cognitive impairment and Alzheimer’s disease

Background: Visuo-spatial and problem-solving abilities are commonly impaired in patients with Alzheimer’s disease (AD). Conversely, subjects with amnestic mild cognitive impairment (aMCI) do not exhibit overt involvement of cognitive domains other than memory. Consequently, a detection of an impairment at the Raven’s colored progressive matrices (RCPM) could be useful to discriminate aMCI from AD and to mark the progression from one condition to another. Aim of the study: To describe the pattern of errors at RCPM in subjects suffering from AD as compared with that of aMCI. Methods: Fifteen patients with AD, 15 subjects with aMCI and 31 Healthy Controls (HC) received the RCPM. The errors were classified as: (1) difference (D); (2) inadequate individuation (II); (3) repetition of the pattern (RP); (4) incomplete correlation (IC). Results: No difference approached significance between aMCI subjects and HC. AD patients always exhibited a higher number of errors as compared with HC. AD patients showed higher number of errors as compared with aMCI only on RP and IC errors. Conclusions: The results suggest that the visuo-spatial and problem-solving impairment that characterize AD, and probably subtend the progression from aMCI to dementia, do not affect to the same extent all cognitive dimensions explored by RCPM