Odmar Neumann

Direct parameter specification and the concept of perception.

SummaryStimuli that reach the sensory surface may result in perception, or serve to guide action. How are these two potential consequences of sensory stimulation related? I discuss three aspects of this problem. Theconceptual aspect concerns the status of the concept of perception in an objective psychology. Themethodological aspect pertains to the problem of how psychophysics is related to the assessment of performance measures. Thefunctional aspect relates to the function(s) of perception for action control. I argue that (a) conceptually, the term perception belongs to a different level of description than the constructs of information-processing models; (b) methodologically, psychophysical judgements and performance measures are not necessarily converging operations; (c) functionally, sensory information can be used for the control of action without perception as a mediating stage (direct parameter specification). Taken together, this suggests that perception should be conceptualized not as a processing stage, but as a class of actions that serve to establish and update an internal representation of the enviroment.

Visual selective attention: Introductory remarks

Theories of selective attention are often put forward as having, in intent, equivalent application to audition, to vision, and, for that matter, to information processing in all other sensory modalities. However, there are certain fundamental differences in the character of information processing in vision and audition; the wiser, or at least the more cautious strategy, may be to concentrate, first of all, on developing models of the selective processes within the different senses individually. Only then, when our understanding of selection within these functionally very different modalities is more secure, will it perhaps be fruitful to look for generalizations about the selection mechanisms across different sensory systems. Accordingly, this special issue is devoted exclusively to studies on selective attention in vision. The early ideas on selective attention, within the information-processing framework, were shaped principally by work on auditory selection, in particular by the demands of selection among concurrent speech signals. In part, this was due to the human engineering context in which modern research on attention evolved. However, there was also a widespread belief that hearing is, because of its functional properties, especially suited to the study of attentional selection. This was, for example, the main message in the introductory chapter of Broadbents (1958) influential monograph, the argument being that auditory selection is almost completely central, whereas peripheral sensory adjustments play a large part in visual selection. In the decades during which modern attention research took shape, theories of attention were thus essentially theories of auditory attention. When attention research began to be extended to the visual modality, many of the central ideas and theoretical alternatives had already been formulated, and theorizing continued to be influenced by them. Meanwhile as witnessed by the contributions to this special issue visual attention has come of age as a research field; it may be timely to consider its particular functional basis. One first step towards adequate theorizing about visual attention is to consider in which respects visual information processing is different from auditory information processing. The properties of vision that are potentially relevant to our understanding of visual attention, and that we

Intentions Determine the Effect of Invisible Metacontrast-Masked Primes: Evidence for Top-Down Contingencies in a Peripheral Cuing Task.

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 primes effect depended on whether it was associated with the same response as the target or with an opposite response.

Differential effects of visual-spatial attention on response latency and temporal-order judgment

SummaryTheorists from both classical structuralism and modern attention research have claimed that attention to a sensory stimulus enhances processing speed. However, they have used different operations to measure this effect, viz., temporal-order judgment (TOJ) and reaction-time (RT) measurement. We report two experiments that compared the effect of a spatial cue on RT and TOJ. Experiment 1 demonstrated that a nonmasked, peripheral cue (the brief brightening of a box) affected both RT and TOJ. However, the former effect was significantly larger than the latter. A masked cue had a smaller, but reliable, effect on TOJ. In Experiment 2, the effects of a masked cue on RT and TOJ were compared under identical stimulus conditions. While the cue had a strong effect on RT, it left TOJ unaffected. These results suggest that a spatial cue may have dissociable effects on response processes and the processes that lead to a conscious percept. Implications for the concept of direct parameter specification and for theories of visual attention are discussed.

Temporal parameters and time course of perceptual latency priming

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.

Temporal, but not spatial, context modulates a masked prime's effect on temporal order judgment, but not on response latency.

Abstract 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 shapes 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 primes effect in the TOJ task, although the prime affected RT under identical conditions. It is concluded that partially different mechanisms mediate the primes 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.

A dissociation between reaction time to sinusoidal gratings and temporal-order judgment

The effect of the spatial frequency (SF) of visual gratings on reaction time (RT) and temporal-order judgment (TOJ) was examined in three experiments. In experiment 1 the visual stimuli were vertical sinusoidal gratings with SFs between 2 and 8 cycles deg−1 and the comparison stimulus in the TOJ task was a 2300 Hz tone. Whereas SF had a highly significant effect on RT, it left TOJ completely unaffected. To test whether this dissociation was due to the sharp (high SF) horizontal edges of the gratings, a second experiment was carried out with circular stimuli with no sharp edges. These stimuli did produce an effect of SF on TOJ, but it was significantly smaller than was the effect on RT. In experiment 3 we confirmed that this difference was not due to differences in grating orientation between the first two experiments. These findings (a) solve discrepancies between findings reported in the literature and (b) strongly suggest that RT and TOJ cannot be regarded as converging operations for determining ‘visual latency’. This dissociation can best be accounted for by assuming that the output of early stimulus analysis can feed directly into the motor system (direct parameter specification), whereas the conscious representation that is used for TOJ is based on later integrative processes.

Apparent distance reduction with moving stimuli (Tandem Effect): Evidence for an attention-shifting model

SummaryWhen two vertical rods move through a horizontal window in close succession, the Tandem Effect can be observed. It consists of a spatial illusion (distance between the rods looking smaller than it actually is) and a temporal illusion (under certain conditions both rods are seen simultaneously in the window, though the first rod has left the window before the second rod enters it). We report six experiments that explored the distance-reduction illusion and tested an attentional model of the effect. It assumes that attention is initially focused on the first rod and then shifted to the second, when it enters the window. The percept of the pair of rods is integrated from the first rods position at the beginning, and the second rods position at the end, of the focus shift. Consequently their subjective distance will be smaller than their physical distance by the distance that they travel during the focus shift. Experiments 1 and 2 established the Tandem Effect as an empirical phenomenon and showed that its size depends on stimulus parameters such as window size and movement speed. Experiments 3–5 tested specific predictions from the attentional model. Experiment 6 examined a further illusion, the Fröhlich Effect, and showed that it can be subsumed under the model. The experiments produced some unexpected effects and some predictions from the model were only partly confirmed. It is shown that the main findings can be combined into two quantitative functions that describe the course of focusing. One implication is that visual attention does not “move” from one object to another; rather all attention shifts originate in the fovea. We discuss several alternative interpretations of our data and show that they are less satisfactory than the attentional model.

Electrophysiological activation by masked primes: Independence of prime-related and target-related activities.

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).

Sensorimotor Supremacy: Investigating Conscious and Unconscious Vision by Masked Priming

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.