This book presents a multidisciplinary approach to the study of relationships between perception and action. It reflects the renewed interest in problems of action control that has emerged in psychology during the last decade and created a new theoretical climate bringing psychology closer to the biological sciences. Each chapter presents both a particular point of view and a comprehensive overview of recent findings relevant to the author's approach.

According to the sensorimotor supremacy hypothesis, conscious perception draws on motor action.In the present report, we will sketch two lines of potential development in the field of masking research based on the sensorimotor supremacy hypothesis.In the first part of the report, evidence is reviewed that masked, invisible stimuli can affect motor responses, attention shifts, and semantic processes.After the review of the corresponding evidence -so-called masked priming effects -an approach based on the sensorimotor supremacy hypothesis is detailed as to how the question of a unitary mechanism of unconscious vision can be pursued by masked priming studies.In the second part of the report, different models and theories of backward masking and masked priming are reviewed.Types of models based on the sensorimotor hypothesis are discussed that can take into account ways in which sensorimotor processes (reflected in masked priming effects) can affect conscious vision under backward masking conditions.

The U-shaped metacontrast function may result from the superimposition of two monotonic components which reflect the effects of mechanisms similar to the peripheral and central processes suggested for backward pattern masking by Turvey (Psychol Rev 80:1–52, 1973). In an experiment using the disc-ring paradigm, it was demonstrated that the decreasing and increasing branches of the metacontrast function are differently affected by the exposure duration of the mask and a task-irrelevant stimulus (distractor) appearing in the contralateral visual hemifield. The phenomenal representation of masking is different for the two parts of the curve. It is suggested that masking in the second part of the masking function, but not in the first, is related to the control of visual attention.

Visual stimuli that are made invisible by metacontrast masking (primes) have a marked influence on behavioral and psychophysiological measures such as reaction time (RT) and the lateralized readiness potential (LRP). 4 experiments are reported that shed light on the effects that masked primes have on the LRP. Participants had a go-nogo task in which the prime was associated with 1 of 2 responses even if the target required participants to refrain from responding. To analyze the electrophysiological responses, we computed the LRP and applied an averaging method separating the activation due to the prime and the target. The results demonstrated that (a) masked primes activate responses even in a nogo situation, (b) this prime-related activation is independent of masking, (c) and is also independent of whether prime and target require the same responses (congruent condition) or different responses (incongruent condition).

The Fehrer–Raab effect (simple reaction time is unaffected by metacontrast masking of the test stimulus) seems to imply that a stimulus can trigger a voluntary reaction without reaching a conscious representation. However, it is also possible that the mask triggers the reaction, and that the masked test stimulus causes a focussing of attention from which processing of the mask profits, thus reaching conscious representation earlier. This is predicted by the Weather Station Model of visual masking. Three experiments tested this explanation. Experiment 1 showed that the masked test stimulus caused a temporal shift of the mask. Experiment 2 showed that the reaction in the Fehrer–Raab effect was not exclusively triggered by a conscious representation of the test stimulus: the mask was involved in evoking the reaction. Experiment 3 again revealed a temporal shift of the mask. However, the shift was only about half as large as the Fehrer–Raab effect. The psychometric functions suggested that the observers used two different cues for their temporal order judgments. The results cast doubts on whether judged temporal order yields a direct estimate of the time of conscious perception. Some methodological alternatives are discussed.

In 5 experiments, the authors tested whether the processing of nonconscious spatial stimulus information depends on a prior intention. This test was conducted with the metacontrast dissociation paradigm. Experiment 1 demonstrated that masked primes that could not be discriminated above chance level affected responses to the visible stimuli that masked them. Experiments 2 and 3 showed that this effect was abolished when the task instruction was changed in such a way that the primes ceased to be task relevant. Experiments 4 and 5 demonstrated that a prime's effect depended on whether it was associated with the same response as the target or with an opposite response.

Visual stimuli (primes) reduce the perceptual latency of a target appearing at the same location (perceptual latency priming, PLP). Three experiments assessed the time course of PLP by masked and, in Experiment 3, unmasked primes. Experiments 1 and 2 investigated the temporal parameters that determine the size of priming. Stimulus onset asynchrony was found to exert the main influence accompanied by a small effect of prime duration. Experiment 3 used a large range of priming onset asynchronies. We suggest to explain PLP by the Asynchronous Updating Model which relates it to the asynchrony of 2 central coding processes, preattentive coding of basic visual features and attentional orienting as a prerequisite for perceptual judgments and conscious perception.

Four experiments investigated the influence of a metacontrast-masked prime on temporal order judgments. The main results were (1) that a masked prime reduced the latency of the mask's conscious perception (perceptual latency priming), (2) that this effect was independent of whether the prime suffered strong or weak masking, (3) that it was unaffected by the degree of visual similarity between the prime and the mask, and that (4) there was no difference between congruent and incongruent primes. Finding (1) suggests that location cueing affects not only response times but also the latency of conscious perception. (2) The finding that priming was unaffected by the prime's detectability argues against a response bias interpretation of this effect. (3) Since visual similarity had no effect on the prime's efficiency, it is unlikely that sensory priming was involved. (4) The lack of a divergence between the effects of congruent and incongruent primes implies a functional difference between the judgments in the temporal order judgment task and speeded responses that have demonstrated differential effects of congruent and incongruent primes (e.g., Klotz & Neumann, 1999). These results can best be interpreted by assuming that the prime affects perceptual latency by initiating a shift of attention, as suggested by the Asynchronous Updating Model (AUM; Neumann 1978, 1982).

In recent years it has been suggested that processing of visual information is divided between a ventral stream, responsible for object recognition and conscious processing of object properties, and a dorsal stream mediating automatic integration of visual information into a motor task. We used metacontrast masking to prevent conscious perception of visual cues concerning the load of an object to be lifted in a precision grip. It was found that when such non-consciously perceived cues warned of a load change, they allowed the subjects to produce the grip force profile appropriate to the new load. It is concluded that non-consciously perceived visual information can be utilised to adapt a functional motor task to actual conditions.

Three experiments investigated a dissociation originally described by Neumann, Esselmann, and Klotz. Stimuli were geometric shapes, preceded by similar shapes that were masked by metacontrast. Each experiment consisted of three parts. In the reaction time (RT) part, participants saw an array of geometric shapes, one of which was marked by bars, and had to respond to the marked shape's position by pressing an appropriate button. A prime (a similar, but smaller stimulus) preceded either the marked or an unmarked stimulus. In the temporal order judgment (TOJ) part, the task was to judge the temporal order of the marked and the unmarked stimulus. In the detection part, detectability of the prime was tested. Although its detectability was zero or close to zero, the prime affected both RT and the apparent onset as measured by TOJ. The effect on RT was significantly larger than the effect on TOJ (Exp. 1). Increasing the spatial context (number of non-target stimuli in the display) did not affect this pattern (Exp. 2). By contrast, reducing the temporal context (range of stimulus onset asynchronies) abolished the prime's effect in the TOJ task, although the prime affected RT under identical conditions. It is concluded that partially different mechanisms mediate the prime's effect in the two tasks and that the effect of stimulus context on TOJ found in the Neumann et al. study was due to temporal, not spatial context.

Nine experiments investigated motor responses to geometric stimuli (a target and a distractor) preceded by masked primes. In congruent trials, the target was preceded by a smaller target-like shape and the distracter by a smaller distracter-like shape. In incongruent trials this arrangement was reversed. In neutral trials both primes were distracter-like shapes. Highly significant effects of these priming conditions on reaction time and error rate were found, although there was no conscious discrimination of primes, as assessed by a discrimination index (d' or d(s)) not different from 0. This result subsisted under conditions of time pressure, feedback, practice, and financial incentive in the discrimination task. It remained unchanged under conditions in which the reaction time and discrimination tasks were blocked, alternated, randomly mixed, or combined on each trial. It is concluded that motor activation without conscious discrimination was demonstrated.

For about half a century, studies of "subliminal perception" have been besieged by two problems. First, the very existence of the phenomenon has been doubtful, and second, it was - if it existed - difficult to integrate into a theoretical framework. We argue that the situation is presently changing in both respects. There are now various observations from neuropsychology demonstrating that sensory information can be processed and used in the control of behavior without being represented in consciousness (e.g., blindsight, visual form agnosia). A similar dissociation (the Metacontrast Dissociation) can be induced in healthy people when a visual stimulus is masked by metacontrast. Under appropriate masking conditions, both behavioral (RT, error rate) and EEG data (lateralized readiness potentials) indicate that the masked stimulus affects motor activation although it cannot be consciously perceived according to the strictest criterion (a d' of zero). At a theoretical level, the Metacontrast Dissociation may be viewed as an example of the more general phenomenon of direct parameter specification (Neumann, 1989, 1990 a); and it could in part be related to the functional differentiation between a dorsal and a ventral stream of visual processing (Milner & Goodale, 1995).

As reported by Neumann and Klotz [1994, in Attention and Performance XV: Conscious and Nonconscious Information Processing Eds C Umiltà, M Moscovitch (Cambridge, MA: MIT Press) pp 123–150], a geometric shape masked by metacontrast can affect response latency (RT) even if it is not visible, ie if it yields a d' value of zero in a signal-detection (SD) task (metacontrast dissociation). In the initial study as well as in most subsequent experiments, the RT task was manual and the SD task was verbal. Hence tasks and output modes were confounded. In the present study, two experiments were conducted to find out which of these factors is responsible for the metacontrast dissociation. In experiment 1, participants performed an RT task in either a manual or a verbal output mode. In experiment 2, these output modes were compared in an SD task. Independently of output modes, the masked primes affected RT but could not be detected in the SD task. It is concluded that tasks, but not output modes, are crucial for the metacontrast dissociation. Implications for the mechanisms underlying the metacontrast dissociation and for the functional difference between judgments and responses are discussed.