Multiscale Discriminant Saliency for Visual Attention

The bottom-up saliency, an early stage of humans' visual attention, can be considered as a binary classification problem between center and surround classes. Discriminant power of features for the classification is measured as mutual information between features and two classes distribution. The estimated discrepancy of two feature classes very much depends on considered scale levels; then, multi-scale structure and discriminant power are integrated by employing discrete wavelet features and Hidden markov tree (HMT). With wavelet coefficients and Hidden Markov Tree parameters, quad-tree like label structures are constructed and utilized in maximum a posterior probability (MAP) of hidden class variables at corresponding dyadic sub-squares. Then, saliency value for each dyadic square at each scale level is computed with discriminant power principle and the MAP. Finally, across multiple scales is integrated the final saliency map by an information maximization rule. Both standard quantitative tools such as NSS, LCC, AUC and qualitative assessments are used for evaluating the proposed multiscale discriminant saliency method (MDIS) against the well-know information-based saliency method AIM on its Bruce Database wity eye-tracking data. Simulation results are presented and analyzed to verify the validity of MDIS as well as point out its disadvantages for further research direction.Comment: 16 pages, ICCSA 2013 - BIOCA sessio

Action Intentions: Action Influences Both On-Line Perception and Off-Line Representation

Given that one role of vision is to gather information for upcoming tasks, previous studies have investigated whether the preparation for action affects visual behaviour. The current studies aimed to determine if such influences on visual selection would also influence the formation of subsequent memory representations. Two experiments were conducted- in the first, participants' action intentions towards a scene were manipulated by the performance of different grasping postures as they observed the scene. This was followed by a memory test for the objects presented. Participants' eye movements were affected by their action intention, so that performing a power grip led to significantly longer fixation durations on power grip compatible objects. In contrast, memory for the objects and their properties was not affected by the action. Our second study required participants to make the action posture during the recall phase. No effect on eye movements was found, but recall was affected, with a particular advantage for recall of the position of grip-compatible objects. Previous studies have shown that action intentions can affect the on-line perception of objects. The current study suggests this may not extend to off-line representations if they are accessed after the action has been completed or abandoned. However, the recall of information may be affected if gestures are formed during retrieval. Memory representations may not be tailored specifically to an action, but actions can still affect the recall of information

Multiple Gaze Cues and Their Effect on Observer Eye Movements in a Visual Search Task

Responses to Posner-type tasks are well documented. Whether presented with a schematic or realistic face, observers seem to reflexively follow the eye movements of the face even when they have been instructed not to do so. However, these tasks do not necessarily elicit the same behaviour as seen in the real world, where gaze cues come with the context of a whole body and often simultaneously with many other cues. We examined search behaviour in realistic scenes with two individuals present. Each individual in the scene cued either the target or a distractor within an array of 15 everyday objects. Unlike results from traditional paradigms, observers rarely fixated on either individual – fixations on the head or body occurring in only 4.38% of trials. Regardless of the lack of overt gaze-following, participants' eye movements were still influenced by gaze cue direction. First saccades were more likely to be directed towards, and land closer to, the target when it was cued by both individuals in the scene. Multiple cues towards the target also improved search efficiency, with scan path ratios closer to 1 when both individuals cued the target. It seems that greater search benefits are produced when targets are cued by both individuals rather than one or neither. We conclude participants' responses are guided covertly by gaze cue information, even though this information is not actively sought out

How context information and target information guide the eyes from the first epoch of search in real-world scenes

This study investigated how the visual system utilizes context and task information during the different phases of a visual search task. The specificity of the target template (the picture or the name of the target) and the plausibility of target position in real-world scenes were manipulated orthogonally. Our findings showed that both target template information and guidance of spatial context are utilized to guide eye movements from the beginning of scene inspection. In both search initiation and subsequent scene scanning, the availability of a specific visual template was particularly useful when the spatial context of the scene was misleading and the availability of a reliable scene context facilitated search mainly when the template was abstract. Target verification was affected principally by the level of detail of target template, and was quicker in the case of a picture cue. The results indicate that the visual system can utilize target template guidance and context guidance flexibly from the beginning of scene inspection, depending upon the amount and the quality of the available information supplied by either of these high-level sources. This allows for optimization of oculomotor behavior throughout the different phases of search within a real-world scene

Disentangling the effects of spatial inconsistency of targets and distractors when searching in realistic scenes

Previous research has suggested that correctly placed objects facilitate eye guidance, but also that objects violating spatial associations within scenes may be prioritized for selection and subsequent inspection. We analyzed the respective eye guidance of spatial expectations and target template (precise picture or verbal label) in visual search, while taking into account any impact of object spatial inconsistency on extrafoveal or foveal processing. Moreover, we isolated search disruption due to misleading spatial expectations about the target from the influence of spatial inconsistency within the scene upon search behavior. Reliable spatial expectations and precise target template improved oculomotor efficiency across all search phases. Spatial inconsistency resulted in preferential saccadic selection when guidance by template was insufficient to ensure effective search from the outset and the misplaced object was bigger than the objects consistently placed in the same scene region. This prioritization emerged principally during early inspection of the region, but the inconsistent object also tended to be preferentially fixated overall across region viewing. These results suggest that objects are first selected covertly on the basis of their relative size and that subsequent overt selection is made considering object-context associations processed in extrafoveal vision. Once the object was fixated, inconsistency resulted in longer first fixation duration and longer total dwell time. As a whole, our findings indicate that observed impairment of oculomotor behavior when searching for an implausibly placed target is the combined product of disruption due to unreliable spatial expectations and prioritization of inconsistent objects before and during object fixation.</p