Functional properties of distractor-induced blindness
Final Report Abstract
Using a novel experimental design, we examined the prerequisites of awareness for simple visual features. Ur task required the detection of the onset of motion coherence which coincides or followed the presentation of a color cue. The presence of distractors (here: episodes of coherent motion preceding the cue) reduced the probability to detect the target significantly. The paradigm has been labelled ‘attention-induced motion blindness’. In our research project, we aimed to answer the following the questions: (1) Is the conscious detection of the target stimulus determined by the level of activation at the sensory level? Following ‘sensory-threshold’ models, conscious detection of a visual target is determined by the level of activation in the sensory cortex. In psychophysical experiments, we therefore varied the physical parameters defining the salience of the target (here: level of motion coherence). Both experiments indicate that motion blindness is not affected by the local motion energy of target. This result was in line with our previous ERP results. (2) Is the lack of awareness for the target related to a competition between the processing costs of cue and target? Our design requires the processing of two relevant events (cue and target), and therefore shares the characteristics of a dual task. Since processing of the cue will load on the common attentional resources of the visual system, processing of the target might be attenuated. Our experiments indicate such a process does not contribute to motion blindness: First, we changed the properties of the visual cue. Motion blindness was also obtained, if the shift from cue to target processing was not associated with a deployment of visuo-spatial attention. Second, we changed the modality of the cue. The effect of motion blindness, and its dependence on distractors, was confirmed is the visual cue was substituted by an auditory cue. (3) Is the (de-) activation of a higher-order control system necessary to gain explicit access to relevant visual information? Our previous studies already indicated that motion blindness is related to a selective filtering of information at a central level. Distractors trigger a cumulative inhibition mechanism, and a corresponding carry-over effect determines the time course of motion blindness. Our experiments confirmed and specified this model: In a series of psychophysical experiments we showed that the process of motion blindness extends to other visual features (here: changes in line orientation). Furthermore, the results indicate a feature-specific inhibition process: The distractor effect depends on the physical similarity to the predefined target. Our ERP studies demonstrate that a unique correlate of the distractor processing is reflected in a frontal negativity. The amplitude of this negativity increased monotonically with increasing number of distractors. This ERP effect, however, was only restricted to trials in which the upcoming target was not identified. In sum, our paradigm allows us to examine the transition of unconscious to conscious visual processing. The probability to get conscious access critically relies on a postperceptual process which inhibits the processing of visual features. The process is feature-specific, and depends on the specification of the target feature. The ERP correlates of the activation of the inhibitory process may serve as a predictor for visual awareness of a simple visual target stimulus.
Publications
- (2009). Inhibition related impairments of coherent motion perception in the attention-induced motion blindness paradigm. Spat Vis, 22(6), 493-509
Hesselmann, G., Allan, J. L., Sahraie, A., Milders, M., & Niedeggen, M.
