Direct Parameter Specification Research Articles

The power of the feed-forward sweep

Vision is fast and efficient. A novel natural scene can be categorized (e.g. does it contain an animal, a vehicle?) by human observers in less than 150 ms, and with minimal attentional resources. This ability still holds under strong backward masking conditions. In fact, with a stimulus onset asynchrony of about 30 ms (the time between the scene and mask onset), the first 30 ms of selective behavioral responses are essentially unaffected by the presence of the mask, suggesting that this type of “ultra-rapid” processing can rely on a sequence of swift feed-forward stages, in which the mask information never “catches up” with the scene information. Simulations show that the feed-forward propagation of the first wave of spikes generated at stimulus onset may indeed suffice for crude re-cognition or categorization. Scene awareness, however, may take significantly more time to develop, and probably requires feed-back processes. The main implication of these results for theories of masking is that pattern or metacontrast (backward) masking do not appear to bar the progression of visual information at a low level. These ideas bear interesting similarities to existing conceptualizations of priming and masking, such as Direct Parameter Specification or the Rapid Chase theory.

The role of direct parameter specification and attentional capture in near-threshold priming of motor reactions

The priming of motor responses can be induced by preceding visual stimuli that have been made invisible by metacontrast masking ('primes'). According to the concept of direct parameter specification( DPS;Neumann,1990),strong similarity between prime and target results in the processing operations that are to be applied to the target being also induced by the prime. As targets have to be attended to, this also implies that attention is captured by the location of a prime, thereby facilitating motor priming effects. This hypothetical effect may be viewed as a form of top-down attentional capture. In some subliminal priming experiments (e.g. Jaśkowski, Skalska, & Verleger, 2003), however, attentional capture may have been unrelated to target identity, as stimuli with unique features (singletons) are known to induce bottom-up attentional capture. Three experiments were performed that largely confirmed the view that the results of these earlier experiments were due to top-down attentional capture, in line with DPS. However, the priming effect was also evoked by a singleton irrelevant to the participants' task, although this effect was weaker than in case of strong similarity between prime and target. Priming effects remained when singletons were absent from one side of the visual field, suggesting that the presence of singletons is not a requirement for the observation of motor priming effects.

Top-down contingencies of nonconscious priming revealed by dual-task interference.

According to the direct parameter specification (DPS) account, reaction time effects of invisible primes depend on top-down control settings directed to targets (Neumann & Klotz, 1994). If this hypothesis holds, effects of invisible primes should decrease in dual-task as compared with single-task conditions: Prior to the primes control settings for the alternative task should be activated, which renders a match between target-directed control settings and primes less likely. In Experiments 1-2 and 4-5, a second task interfered with the validity effect of invisible primes. Control conditions ruled out several alternative explanations. Interference was not due to higher spatial memory loads (Experiments 1 vs. 2), increased numbers of stimuli or responses (Experiments 3-5), or increased response latencies (Experiment 3). If predictable, alternative tasks did not interfere (Experiment 3). The results are in line with the DPS account and less so with some classical definitions of automatic processing (e.g., Posner & Snyder, 1975).

Direct parameter specification of an attention shift: evidence from perceptual latency priming

In the direct parameter specification (DPS) mode of sensorimotor control, response parameters can be specified by stimuli that are not consciously perceived [Psychological Research/Psychologische Forschung 52 (1990) 207]. DPS is contingent on the current intentions. The invisible stimuli can be processed for the purposes of sensorimotor control only if they match the actual intentions, for example, share task-relevant features. The present experiments explore whether attentional capture by masked abrupt-onset stimuli is mediated via DPS. Participants judged which of two visual targets appeared first. Masked primes preceded one of the targets. The primes were either similar to the targets or not, in shape, or in color. Target-like (task-relevant), but not distractor-like (task-irrelevant), primes facilitated perceptual latencies of targets trailing at their positions. Thus, the latency effects resulted from DPS of an attention shift, rather than from bottom-up capture or from top-down search for dynamic features.

Influences of visibility, intentions, and probability in a peripheral cuing task

According to the concept of direct parameter specification, nonconsciously registered information can be processed to the extent that it matches currently active intentions of a person. This prediction was tested and confirmed in the current study. Masked visual information provided by peripheral cues led to reaction time (RT) effects only if the information specified one of the required responses (Experiments 1 and 3). Information delivered by the same masked cues that did not match the intentions was not used. However, the same information influenced RT if it was provided by visible cues (Experiments 2 and 3). The results suggest that the processing of nonconsciously registered information is flexible because it is susceptible to the changing intentions of a person. Yet, these processes are apparently restricted, as nonconsciously registered information cannot be used as easily for purposes not corresponding to the currently active intentions as better visible information.

Relationship between flanker identifiability and compatibility effect.

What is the relation between the identifiability of masked flankers and their ability to induce compatibility effects in a letter classification task? Using a within-subjects design (n = 8), we first determined identification performance for two flankers (H or N) around an irrelevant target letter as a function of the time (stimulus onset asynchrony, or SOA) after which the flankers were masked. In a second condition, subjects classified the central letter of the same stimulus patterns irrespectively of the identity of the flankers. The compatibility effects increased with increasing identification performance as a function of SOA, and we found a significant compatibility effect even at an SOA at which the identifiability of the flankers did not differ significantly from zero. We discuss the statistical power of our design and an interpretation of our results in terms of a dissociation between perceptual processes and processes directly activating the motor system (direct parameter specification; cf. Neumann, 1990).

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.

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

Theorists 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.

Direct parameter specification and the concept of perception

Stimuli 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. The conceptual aspect concerns the status of the concept of perception in an objective psychology. The methodological aspect pertains to the problem of how psychophysics is related to the assessment of performance measures. The functional 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 environment.