Dietmar Heinke

Early, Involuntary Top-Down Guidance of Attention From Working Memory

Four experiments explored the interrelations between working memory, attention, and eye movements. Observers had to identify a tilted line amongst vertical distractors. Each line was surrounded by a colored shape that could be precued by a matching item held in memory. Relative to a neutral baseline, in which no shapes matched the memory item, search was more efficient when the memory cue matched the shape containing the target, and it was less efficient when the cued stimulus contained a distractor. Cuing affected the shortest reaction times and the first saccade in search. The effect occurred even when the memory cue was always invalid but not when the cue did not have to be held in memory. There was also no evidence for priming effects between consecutive trials. The results suggest that there can be early, involuntary top-down directing of attention to a stimulus matching the contents of working memory.

Attention, spatial representation, and visual neglect: Simulating emergent attention and spatial memory in the Selective Attention for Identification Model (SAIM)

The selective attention for identification model (SAIM) is presented. This uses a spatial window to select visual information for recognition, binding parts to objects and generating translation-invariant recognition. The model provides a qualitative account of both normal and disordered attention. Simulations of normal attention demonstrate 2-object costs and effects of object familiarity on selection, global precedence, spatial cueing, and inhibition of return. When lesioned, SAIM demonstrated either view- or object-centered neglect or spatial extinction, depending on the type and extent of lesion. The model provides a framework to unify (a) object- and space-based theories of normal selection, (b) dissociations within the syndrome of unilateral neglect, and (c) attentional and representational accounts of neglect.

Working memory can guide pop-out search.

Top-down feedback from working memory (WM) can exert an early and involuntary influence on visual selection for targets that are relatively difficult to discriminate [Soto, D., Heinke, D., Humphreys, G. W., & Blanco, M. J. (2005) Journal of Experimental Psychology: Human Perception and Performance, 31, 248]. Here, we demonstrate similar effects even on search for a pop-out target. At the beginning of each trial, participants memorized a prime that could contain either the search target or a distracter in the subsequent search array. Targets and distractors were easily discriminable. Despite this, the prime in WM affected responses latencies and the direction of the first saccade. Top-down search, guided by the contents of WM, can modulate selection even when salient bottom-up cues are present.

Modelling direct perceptual constraints on action selection: The Naming and Action Model (NAM)

There is increasing experimental and neuropsychological evidence that action selection is directly constrained by perceptual information from objects as well as by more abstract semantic knowledge. To capture this evidence, we develop a new connectionist model of action and name selection from objects — NAM (Naming and Action Model), based on the idea that action selection is determined by convergent input from both visual structural descriptions and abstract semantic knowledge. We show that NAM is able to simulate evidence for a direct route to action selection from both normal subjects (Experiments 1 and 2) and neuropsychological patients (Experiments 3-6). The model provides a useful framework for understanding how perceptual knowledge influences action selection.

Comparing neural networks: a benchmark on growing neural gas, growing cell structures, and fuzzy ARTMAP

This article compares the performance of some recently developed incremental neural networks with the wellknown multilayer perceptron (MLP) on real-world data. The incremental networks are fuzzy ARTMAP (FAM), growing neural gas (GNG) and growing cell structures (GCS). The real-world datasets consist of four different datasets posing different challenges to the networks in terms of complexity of decision boundaries, overlapping between classes, and size of the datasets. The performance of the networks on the datasets is reported with respect to measure classification error, number of training epochs, and sensitivity toward variation of parameters. Statistical evaluations are applied to examine the significance of the results. The overall performance ranks in the following descending order: GNG, GCS, MLP, FAM.

Dividing the mind: the necessary role of the frontal lobes in separating memory from search.

Working memory plays a crucial role in the control of visual selection. Previous research has shown that attentional deployment can be biased to objects in an array matching the contents of working memory. Here, we examined the role of the frontal cortex in determining the interaction between working memory and attention. At the start of each trial, participants memorized an object cue that could contain either the target or a distracter, when the object reappeared in the subsequent search array. Relative to age-matched controls, patients suffering from damage to the frontal lobes showed a stronger effect of the memory stimulus on search. Interestingly, there was an effect of frontal damage on the mean latencies to fixate targets but the effect of memory validity on the number of first saccades to the target, and their time of initiation, was similar across the groups. The results suggest that, following the earliest deployment of attention, frontal lobe structures are involved in separating relevant target from irrelevant (object cue) information, when both are held in memory.

Connectionist Models in Cognitive Neuroscience

We review three problems in the connectionist modelling of visual word recognition: the restriction of models to monosyllabic words, the difficulty in assimilating fixation data from the reading of continuous text, and the abstractness of the accounts of dyslexic reading. We show how a model of visual word recognition, the SPLIT model, can be anatomically based on the precise splitting of the foveal projection about a vertical meridian. The SPLIT model has a limited instantiation as a connectionist model and a wider instantiation as a conventional statistical analysis. This combination of two modelling paradigms, both based on foveal splitting, gives the best coverage of word recognition phenomena.

Prioritization in visual search: Visual marking is not dependent on a mnemonic search

Visual marking (VM) refers to our ability to completely exclude old items from search when new stimuli are presented in our visual field. We examined whether this ability reflects an attentional scan of the old items, possibly allowing observers to apply inhibition of return or maintain a memory representation of already seen locations. In four experiments, we compared performance in two search conditions. In the double-search (DS) condition, we required participants to pay attention to a first set of items by having them search for a target within the set. Subsequently, they had to search a second set while the old items remained in the field. In the VM condition, the participants expected the target only to be in the second (new) set. Selection of new items in the DS condition was relatively poor and was always worse than would be expected if only the new stimuli had been searched. In contrast, selection of the new items in the VM condition was good and was equal to what would be expected if there had been an exclusive search of the new stimuli. These results were not altered when differences in Set 1 difficulty, task switching, and response generation were controlled for. We conclude that the mechanism of VM is distinct from mnemonic and/or serial inhibition-of-return processes as involved in search, although we also discuss possible links to more global and flexible inhibition-of-return processes not necessarily related to search.

Featural Guidance in Conjunction Search: The Contrast Between Orientation and Color

Four experiments examined the effects of precues on visual search for targets defined by a color-orientation conjunction. Experiment 1 showed that cueing the identity of targets enhanced the efficiency of search. Cueing effects were stronger with color than with orientation cues, but this advantage was additive across array size. Experiment 2 demonstrated that cueing effects interacted with bottom-up segmentation processes, whereas Experiment 3 showed the stronger effects of color cues remained in a compound task. Experiment 4 confirmed the enhanced effect of color cueing even when verbal rather than visual cues were used. The targets used were balanced for search efficiency within both orientation and color dimensions. We suggest search benefits from the top-down cueing of color compared with orientation because color cueing enhances the segmentation of displays into color groups more efficiently. This enables search to an appropriate color group to be initiated earlier. We discuss how top-down segmentation processes interact with differences in bottom-up segmentation to further improve target detection.

Transient binding by time: Neuropsychological evidence from anti-extinction

Anti-extinction occurs when there is poor report of a single stimulus presented on the contralesional side of space, but better report of the same item when it occurs concurrently with a stimulus on the ipsilesional side (Goodrich & Ward, 1997). We report a series of experiments that examine the factors that lead to anti-extinction in a patient GK, who has bilateral parietal lesions but more impaired identification of left-side stimuli. We show a pattern of anti-extinction when stimuli are briefly presented, which is followed by an extinction effect when stimuli are left for longer in the visual field. In Experiments 1 and 2 we present evidence that the anti-extinction effects are determined by stimuli onsetting together, and it is not apparent when stimuli are defined by offsets. In Experiments 3 and 4 we report that performance is not strongly affected by whether the same or different tasks are performed on the ipsi- and contralesional stimuli, and the anti-extinction effect also survives trials where eye movements are made to right-side stimuli. Experiment 5 provides evidence that anti-extinction is due to temporal grouping between stimuli, rather than to increased arousal or cueing attention to the contralesional side. Experiment 6 demonstrates that anti-extinction dissociates from GKs conscious perception of when contra- and ipsilesional stimuli occur together. We interpret the data as indicating that there is unconscious and transient temporal binding in vision.