Modelling task-dependent eye guidance to objects in pictures

We introduce a model of attentional eye guidance based on the rationale that the deployment of gaze is to be considered in the context of a general action-perception loop relying on two strictly intertwined processes: sensory processing, depending on current gaze position, identi\ufb01es sources of information that are most valuable under the given task; motor processing links such information with the oculomotor act by sampling the next gaze position and thus performing the gaze shift. In such a framework, the choice of where to look next is taskdependent and oriented to classes of objects embedded within pictures of complex scenes. The dependence on task is taken into account by exploiting the value and the payoff of gazing at certain image patches or proto-objects that provide a sparse representation of the scene objects. The different levels of the action-perception loop are represented in probabilistic form and eventually give rise to a stochastic process that generates the gaze sequence. This way the model also accounts for statistical properties of gaze shifts such as individual scan path variability. Results of the simulations are compared either with experimental data derived from publicly available datasets and from our own experiments

Modeling visual attention on scenes

International audienceLa modélisation computationelle de l'attention visuelle connaît actuellement un essor considérable. Les premières modèles, purement basés sur l'attention dite exogène, permettent de calculer une carte de saillance indiquant les zones d'intérêt visuel d'une image. Cependant, afin d'améliorer cette prédiction, il s'avère nécessaire de prendre en compte des informations de plus haut niveaux relatives à l'attention endogène, c'est à dire des informations liées aux processus cognitifs. Afin de rendre compte de cette problématique, le présent article décrit un certain nombre de modèles exogènes ainsi que des modèles intégrant de la connaissance a priori. Les méthodes d'évaluation des performances sont également décrites. Afin d'aller plus loin dans la modélisation et dans la compréhension des processus cognitifs, de nouvelles perspectives et direction d'études sont exposées

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Category-effects and stimulus characteristics in visual perception

This thesis describes a number of experiments that aimed to investigate the role of relatively low-level visual input factors in category-specific effects in object identification and colour perception. In the object recognition experiments, using picture-name or name-picture verification tasks, as well as object-naming tasks, clues to the causal factors contributing to such effects were obtained. It was found that category-specific effects in normal object identification, both living things advantages and living things disadvantages can occur even when nuisance variables like familiarity and complexity are well controlled. Task demands on perceptual differentiation and stimulus presentation conditions can influence and even reverse category-specific effects (Report I). When identification has to rely mostly on global shape visual information, the living things advantage in identification is enhanced compared to when visual detail is available in stimulus pictures. Furthermore, a lack of visual detail induces a left hemisphere disadvantage for identification, but only for nonliving things (Report II). In an experiment utilising eye movement methods, it was found that when rotating objects in depth, which presumably causes changes in outline shape, changes in participants' eye movement strategies could be observed. Specifically, participants tended to focus more on the objects' centres of gravity when rotations went from canonical to noncanonical views. This effect was, however, only reliably observed for nonliving things. (Report III). In a study examining differential interference effects in Stroop performance, it was found that the amount of interference is smaller for non-opponent compared to opponent colours. An artificial neural network that coarsely implements a trichromatic input coding scheme can simulate this reduced opponent colour interference. Additionally, it was found that individual differences in colour discrimination ability are associated with individual differences in Stroop performance. (Report IV)