Breaking the rules in perceptual information integration.

We develop a broad theoretical framework for modelling difficult perceptual information integration tasks under different decision rules. The framework allows us to compare coactive architectures, which combine information before it enters the decision process, with parallel architectures, where logical rules combine independent decisions made about each perceptual source. For both architectures we test the novel hypothesis that participants break the decision rules on some trials, making a response based on only one stimulus even though task instructions require them to consider both. Our models take account of not only the decisions made but also the distribution of the time that it takes to make them, providing an account of speed-accuracy tradeoffs and response biases occurring when one response is required more often than another. We also test a second novel hypothesis, that the nature of the decision rule changes the evidence on which choices are based. We apply the models to data from a perceptual integration task with near threshold stimuli under two different decision rules. The coactive architecture was clearly rejected in favor of logical-rules. The logical-rule models were shown to provide an accurate account of all aspects of the data, but only when they allow for response bias and the possibility for subjects to break those rules. We discuss how our framework can be applied more broadly, and its relationship to Townsend and Nozawa's (1995) Systems-Factorial Technology.

Need for closure is associated with urgency in perceptual decision-making.

Constant decision-making underpins much of daily life, from simple perceptual decisions about navigation through to more complex decisions about important life events. At many scales, a fundamental task of the decision-maker is to balance competing needs for caution and urgency: fast decisions can be more efficient, but also more often wrong. We show how a single mathematical framework for decision-making explains the urgency/caution balance across decision-making at two very different scales. This explanation has been applied at the level of neuronal circuits (on a time scale of hundreds of milliseconds) through to the level of stable personality traits (time scale of years).

Inverse effectiveness and multisensory interactions in visual event-related potentials with audiovisual speech.

In recent years, it has become evident that neural responses previously considered to be unisensory can be modulated by sensory input from other modalities. In this regard, visual neural activity elicited to viewing a face is strongly influenced by concurrent incoming auditory information, particularly speech. Here, we applied an additive-factors paradigm aimed at quantifying the impact that auditory speech has on visual event-related potentials (ERPs) elicited to visual speech. These multisensory interactions were measured across parametrically varied stimulus salience, quantified in terms of signal to noise, to provide novel insights into the neural mechanisms of audiovisual speech perception. First, we measured a monotonic increase of the amplitude of the visual P1-N1-P2 ERP complex during a spoken-word recognition task with increases in stimulus salience. ERP component amplitudes varied directly with stimulus salience for visual, audiovisual, and summed unisensory recordings. Second, we measured changes in multisensory gain across salience levels. During audiovisual speech, the P1 and P1-N1 components exhibited less multisensory gain relative to the summed unisensory components with reduced salience, while N1-P2 amplitude exhibited greater multisensory gain as salience was reduced, consistent with the principle of inverse effectiveness. The amplitude interactions were correlated with behavioral measures of multisensory gain across salience levels as measured by response times, suggesting that change in multisensory gain associated with unisensory salience modulations reflects an increased efficiency of visual speech processing.

The influence of feature conjunction on object inversion and conversion effects.

The face inversion effect is considered by some as a marker ofholistic or configural processing. In an effort to understand the relations between object orientation and the use of configuration for recognition, we explored the extent to which the combination of information across discrete, spatially separated object features contributed to the impact of transforming the orientation of faces and other objects. Subjects performed a matching task on four different sets of faces and novel objects. For two of the sets (diagnostic), the match could be made based on information contained in a single feature. For the remaining two sets (conjunction and disjunction), the information useful for successful matching was divided between two spatially separated features (at the top and at the bottom of the object). For OR disjunctions the top and bottom features provided redundant information such that subjects could rely on either the top or the bottom feature, whereas for AND conjunctions the top and bottom features provided unique information such that subjects needed to use both the top and the bottom features. Experiment 1 assessed the cost of inversion on these stimulus sets with the typical inversion task, where both study and test stimuli were presented in the same orientation. Consistent with previous work, significant inversion effects were found for all of the face sets, but none of the novel object sets. Experiment 2 assessed the cost of 'conversion'--that is, the effect of transforming the orientation of the stimulus between study and test. Consistent with previous work, significant conversion effects were found for all face sets; however, a significant conversion effect was also found for the AND novel set. That only the AND novel set was significant suggests that conversion effects are reliant on combination of information across features, which is compromised when the stimulus configuration is altered between study and test. The results suggest that configural processes, like those purportedly used for face recognition, may be domain-general processes that can also be recruited strategically with other types of objects.