Hughes (1984) has reported that the magnitude of the cue-validity effect in luminance detection is unaffected by target luminance. In three experiments, we explored the possible basis of this counterintuitive finding. The experiments focused on the design of the Hughes study, in which target luminance was treated as a between-blocks variable. Our results reveal that when target luminance is varied randomly within trial blocks, the cue-validity effect grows with declining target luminance. The difference between our findings and those of Hughes is interpreted in terms of cue-utilization strategies, which may adapt to target luminance when luminance remains invariant within trial blocks. Several alternative conceptions of the nature and locus of the cuevalidity effect in luminance detection are considered in light of these results.Posner and his colleagues (e.g., Posner, Nissen, & Ogden, 1978) have devised a simple, yet highly sensitive, procedure for investigating the effects of directed attention in visual target detection. The procedure consists of presenting a cue indicating the likely location of a signal that is to be detected, and then presenting the signal either at the cued location or (occasionally) at an uncued location. Detection latency under these conditions is shorter when the cue is valid than when it is invalid as a predictor of target location.A complication of the basic procedure entails the addition of trials containing a noninformative (neutral) cue. Here, detection latency is often shorter in cued than in neutral trials, yielding what Posner terms an attentional benefit, and slower in uncued than in neutral trials, yielding an attentional cost. These effects hold even in the absence of eye movements (Posner, 1978). Posner has interpreted this pattern of results in terms of the assumptions that cuing directs the covert orientation of attention and that attention enhances the efficiency of sensory processes underlying detection.Recently, Hughes (1984) used the Posner procedure to inquire into the location within the visual system of the processes underlying the cue-validity effect. One of the variables he investigated was target luminance, and he found (1) that reductions in target luminance produce overall increases in target-detection latency, but (2) that the magnitude of the cue validity effect (reaction time, RT, on invalid cue trials minus RT on valid cue trials) Correspondence should be directed to H. L. Hawkins, Perceptual Sciences Program, Office of the Chief of Naval Research, Arlington, VA 22217-5000.does not increase with reductions in target luminance. In fact, the cuing effect was reliably smaller for the lowest target luminance studied than for all others. The latter result was dismissed as the likely result of ceiling effects. Drawing on the logic of additive factors (Sternberg, 1969), Hughes interpreted the observed additivity across all other luminance conditions as showing that signalluminance and directed visual attention operate at separate stages in the signal detection p...

Speech researchers have been attempting to isolate acoustic invariance in the speech signal for the past several decades. Currently, however, no conception of invariance has proven adequate to the task of demonstrating the existence of invariant acoustic features in the six English stop consonants. In the present study, static and dynamic versions of two recent invariance proposals [Sawusch and Dutton (in press) and Forrest, Weismer, Milenkovic, and Dougall (1988)] were developed and tested on a corpus of 1392 naturally produced stop and stop consonant cluster tokens. Classification accuracies of the metrics using stepwise discriminant analyses showed performance to be significantly different from chance but lower than expected had the metrics isolated invariance in the signal. Results will be discussed in terms of general human auditory-phonetic coding ability. Also, the notion that invariant acoustic features are the most useful way of conceptualizing the problem of phoneme recognition will be questioned. [Work supported by NIDCD Grant No. R01-DC00219 to SUNY at Buffalo.]

Spatial phase plays an important role in the characterization of images and other visual patterns. Despite this, relatively few experiments have investigated the role of phase per se in human vision. Recent studies by Kersten (1983) and Burgess and Ghandeharian (1984) have shown that human observers are more sensitive to sinusoidal grating patterns when they have prior knowledge of the pattern's absolute phase than when they do not. They concluded that observers act as phase-sensitive detectors at least some of the time. Two forced-choice sinusoidal grating detection experiments are reported here which extend these results. Absolute signal phase was either held constant or varied randomly across trials. On half of the random-phase trials, observers were shown a sinusoidal grating cue that revealed the absolute phase of the test signal for that trial. There were three major findings. First, detection performance in both experiments was substantially better when phase information was provided than when it was not. This is consistent with previous findings. Second, information about signal phase was provided equally effectively by holding phase constant over all trials within a testing block (as in the constantphase conditions) or by providing an explicit phase cue 250 msec before each trial. Third, a phase cue presented 250 msec after the test pattern offset led to performance levels intermediate between the superior constant-phase condition and the uncued random-phase condition. In other words, observers were able to use phase information even when it was presented in a postcue. The findings are discussed in terms of alternative phase-sensitive detection models.For many years psychophysicists have been interested in the ability of human perceivers to detect visual signals in noise. In a traditional visual detection task, observers are required to judge whether a well-specified visual target, such as a sinusoidal grating pattern, is present on each of a series of trials. Previous research has shown that a wide range of signal and subjective factors can influence the ability of an observer to detect even these simple targets. For example, signal parameters, such as spatial frequency, spatial extent, spatial location, temporal duration, orientation, and phase, are important (Graham, 1985), as are subjective factors, such as condition of dark adaptation, age, and the observer's prior knowledge of the signal. The experiments reported in this paper investigated the role of absolute signal phase and the observer's prior knowledge of phase in the detection of sinusoidal grating patterns embedded in a noise background. In this context, absolute phase refers to the alignment of the sinusoidal pattern (the location oflight bands or peaks) within a viewing field. The Importance of PhaseIt is obvious that spatial phase plays an important role in the characterization of images and other visual patterns.

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