Intentional and unintentional contributions to nonspecific preparation during reaction time foreperiods.

The nonspecific preparation that follows a warning stimulus (WS) to speed responding to an impending imperative stimulus (IS) is generally viewed as a strategic, intentional process. An alternative view holds that WS acts as a conditioned stimulus that unintentionally elicits a tendency to respond at the moment of IS presentation as a result of a process of trace conditioning. These views were contrasted as explanatory frameworks for classical effects on reaction time of the duration and intertrial variability of the foreperiod, the interval between WS and IS. It is shown that the conditioning view accounts for the available data at least as well as the strategic view. In addition, the results of 3 experiments provide support for the conditioning view by showing that unintentional contributions to nonspecific preparation can be dissociated from intentional contributions.

The foreperiod effect revisited: conditioning as a basis for nonspecific preparation.

The foreperiod (FP) is the interval between a warning stimulus and the imperative stimulus. It is a classical finding that both the duration and the intertrial variability of FP considerably affects response time. These effects are invariably attributed to the participant's state of nonspecific preparation at the moment the imperative stimulus is presented. In this article, we examined a proposal by Los, S. A. (1996) [On the origin of mixing costs: exploring information processing in pure and mixed blocks of trials. Acta Psychologica, 94, 145-188] that the real-time development of nonspecific preparation during FP relies on the same principle as trace conditioning. To this end, we adjusted the formal conditioning model developed by Machado, A. (1997) [Learning the temporal dynamics of behavior. Psychological Review, 104 (2), 241-265], and fitted this model to a representative data set we obtained from nine participants. Although the model accounted for only a moderate proportion of the variance, it accurately reproduced several key features of the data. We therefore concluded that the model is a promising first step toward a theory of nonspecific preparation.

Identifying stimuli of different perceptual categories in pure and mixed blocks of trials: evidence for stimulus-driven switch costs.

Responding to stimuli of different perceptual categories is usually faster when the categories are presented isolated from each other, in pure blocks, than when they are presented randomly intermixed, in mixed blocks; a difference denoted as perceptual mixing costs. The present study examined the contribution of strategic and stimulus-driven factors to these costs. The first two experiments showed that perceptual mixing costs were not reduced when participants were informed at the start of each trial in mixed blocks about the impending category. Furthermore, Experiments 1 and 3 showed that mixing costs were concentrated on those trials of mixed blocks where the perceptual category was different from that of the preceding trial. These results support the view that perceptual mixing costs derive from stimulus-driven trial-by-trial adjustments in processing. Some general implications for processing models are discussed.

Identifying stimuli of different perceptual categories in mixed blocks of trials: evidence for cost in switching between computational processes.

Responding to stimuli of different perceptual categories is usually faster when the categories are presented isolated from each other, in pure blocks, than when they are presented intermixed, in mixed blocks. According to criterion models, these perceptual mixing costs result from the use of a less conservative response criterion in pure than in mixed blocks. According to alternate processing models, mixing costs result from time-consuming switching in mixed blocks between different computational processes called on by the different perceptual categories. In 5 experiments, participants had to identify number stimuli of different categories. The results showed clear mixing costs whenever these categories differed in their assumed computational processing requirements but not when they differed on features that seemed trivial from a computational viewpoint. The results favor the alternate processing conception.

Bond strengths and SEM evaluation of Clearfil Liner Bond 2.

PURPOSE: To evaluate a dental adhesive system that uses a single conditioning/primer agent. MATERIALS AND METHODS: Twenty-five flat enamel and dentin bonding sites were prepared to 600 grit on human molar teeth. The Clearfil Liner Bond 2 adhesive system was used to bond Clearfil AP-X composite to both enamel and dentin. After 24 hours of water storage, shear bond strengths were determined using an Instron testing machine. Fifty V-shaped cavity preparations were prepared in human molar teeth with an enamel and cementum margin. Composite restorations were placed using the new adhesive system. The teeth were stored for 24 hours, thermocycled, stained with AgNO3 , sectioned and examined for microleakage. SEM examinations were also completed to evaluate the effects of the treatment steps on enamel and dentin surfaces. RESULTS: Mean shear bond strengths for the experimental adhesive to enamel and dentin were 28.2 +/- 4.9 and 19.4 +/- 3.1 MPa. A t-test revealed that the enamel bond strength was significantly greater (P<0.05) than the dentin strength. No marginal leakage was observed from the enamel margins of the restorations. Three restorations showed minimal leakage from the cementum margins. SEM examinations showed resin penetration into both the conditioned enamel and dentin surfaces. The adhesive system produced high bond strengths to both enamel and dentin, exhibited very minimal microleakage and was easy to use.

Effects of dentin air abrasion with aluminum oxide and hydroxyapatite on adhesive bond strength.

Shear bond strengths to dentin were determined with six current-generation resin adhesive systems following air abrasion of the dentin surface with aluminum oxide and hydroxyapatite. In addition, scanning electron microscopy was used to examine the effects of air abrasive techniques and conditioners/primers on the dentin surfaces. Altering the dentin surface with air abrasion using aluminum oxide and hydroxyapatite did not enhance dentin bond strengths with current-generation adhesive systems. Air abrasion of dentin with aluminum oxide created more surface irregularity than hydroxyapatite. Dentin surfaces air abraded with aluminum oxide and the treated with conditioners that removed the smear layer appeared more irregular than flat ground dentin surfaces treated with the same conditioners.

Procedural differences in processing intact and degraded stimuli.

In three experiments, the extent to which the processing of a visual stimulus profits from equal processing demands of a preceding stimulus was examined. Subjects identified two subsequently presented digits (S1 and S2) that were either intact or degraded by noise, yielding four combinations of stimulus quality. In Experiments 1 and 2, S1 and S2 differed with respect to the values of the digits, so that stimulus quality was the only dimension of possible agreement. The results revealed a faster response to S2 when the stimulus pairs were homogeneous (both intact or both degraded stimuli) than when they were not homogeneous (degraded-intact pairs and intact-degraded pairs, respectively). The occurrence of equal values of S1 and S2 (Experiment 3) tended to magnify this homogeneous-stimulus effect, but was not a prerequisite for its occurrence. Relative to conditions considered to be neutral, the homogeneous-stimulus effect proved to be due to deviant behavior following the processing of a degraded S1. The suggestion that this reflects the involvement of controlled processing is discussed.