To understand how a human operator performs visual search in complex scenes, it is necessary to t... more To understand how a human operator performs visual search in complex scenes, it is necessary to take into account top-down cognitive biases in addition to bottom-up visual saliency effects. We constructed a model to elucidate the relationship between saliency and cognitive effects in the domain of visual search for distant targets in photo-realistic images of cluttered scenes. In this domain, detecting targets is difficult and requires high visual acuity. Sufficient acuity is only available near the fixation point, i.e. in the fovea. Hence, the choice of fixation points is the most important determinant of whether targets get detected. We developed a model that predicts the 2-D distribution of fixation probabilities directly from an image. Fixation probabilities were computed as a function of local contrast (saliency effect) and proximity to the horizon (cognitive effect: distant targets are more likely to be found close to the horizon). For validation, the model’s predictions were ...
For all groups, the Action task elicited worse performance than the Perception task These resul... more For all groups, the Action task elicited worse performance than the Perception task These results suggest that the Action system may be different from the Perception system. The difference in performance between tasks was significantly greater for 3 YO than 7 YO normally developing children This suggests that the Action system matures more slowly than the Perception system, consistent with the proposal that the dorsal stream may mature more slowly than the ventral stream.
The Quarterly Journal of Experimental Psychology Section A, 1993
Four dual-task experiments required a speeded manual choice response to a tone in a close tempora... more Four dual-task experiments required a speeded manual choice response to a tone in a close temporal proximity to a saccadic eye movement task. In Experiment 1, subjects made a saccade towards a single transient; in Experiment 2, a red and a green colour patch were presented to left and right, and the saccade was to which ever patch was the pre-specified target colour. There was some slowing of the eye movement, but neither task combination showed typical dual-task interference (the “psychological refractory effect”). However, more interference was observed when the direction of the saccade depended on whether a central colour patch was red or green, or when the saccade was directed towards the numerically higher of two large digits presented to the left and the right. Experiment 5 examined a vocal second task, for comparison. The findings might reflect the fact that eye movements can be directed by two separate brain systems–-the superior colliculus and the frontal eye fields; comman...
To understand how a human operator performs visual search in complex scenes, it is necessary to t... more To understand how a human operator performs visual search in complex scenes, it is necessary to take into account top-down cognitive biases in addition to bottom-up visual saliency effects. We constructed a model to elucidate the relationship between saliency and cognitive effects in the domain of visual search for distant targets in photo-realistic images of cluttered scenes. In this domain, detecting targets is difficult and requires high visual acuity. Sufficient acuity is only available near the fixation point, i.e. in the fovea. Hence, the choice of fixation points is the most important determinant of whether targets get detected. We developed a model that predicts the 2-D distribution of fixation probabilities directly from an image. Fixation probabilities were computed as a function of local contrast (saliency effect) and proximity to the horizon (cognitive effect: distant targets are more likely to be found close to the horizon). For validation, the model’s predictions were ...
For all groups, the Action task elicited worse performance than the Perception task These resul... more For all groups, the Action task elicited worse performance than the Perception task These results suggest that the Action system may be different from the Perception system. The difference in performance between tasks was significantly greater for 3 YO than 7 YO normally developing children This suggests that the Action system matures more slowly than the Perception system, consistent with the proposal that the dorsal stream may mature more slowly than the ventral stream.
The Quarterly Journal of Experimental Psychology Section A, 1993
Four dual-task experiments required a speeded manual choice response to a tone in a close tempora... more Four dual-task experiments required a speeded manual choice response to a tone in a close temporal proximity to a saccadic eye movement task. In Experiment 1, subjects made a saccade towards a single transient; in Experiment 2, a red and a green colour patch were presented to left and right, and the saccade was to which ever patch was the pre-specified target colour. There was some slowing of the eye movement, but neither task combination showed typical dual-task interference (the “psychological refractory effect”). However, more interference was observed when the direction of the saccade depended on whether a central colour patch was red or green, or when the saccade was directed towards the numerically higher of two large digits presented to the left and the right. Experiment 5 examined a vocal second task, for comparison. The findings might reflect the fact that eye movements can be directed by two separate brain systems–-the superior colliculus and the frontal eye fields; comman...
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Papers by James Hoffman