Detecting conjunctions of color and form in parallel

Certain theories of visual attention assume that at least one processing stage must be serial when the target of search is defined as the conjunction of two or more separable features. To explain why conjunction-search response times do not always form linearly increasing functions of display size, recent versions of this general model have posited the existence of an early parallel process that guides the serial stage toward display elements that are likely targets. Other models have relaxed the seriality assumption, allowing for a limited number of parallel decisions. In the three experiments reported here, a redundant-target detection task was used with conjunctively defined targets and display sizes of two (Experiment 1), one or two (Experiment 2), and six (Experiment 3). In all three experiments, strong evidence for parallel processing was observed. The implications for models of elementary visual processes are discussed.     

Post-response stimulation and the Simon effect: Further evidence of action-effect integration

The recently proposed action-concept view of perceptual-motor behaviour posits that a stimulus which consistently follows a certain response will become associated with that response. Some evidence in favour of this view comes from the finding that the size of the Simon effect can be altered by the inclusion of post-response stimuli. However, only one study has investigated the effects of including same-side in addition to opposite-side post-response stimuli, as well as a neutral Simon condition, and, possibly because of a failure of random assignment, the results from that study were inconclusive. In light of this limitation, a Simon experiment was performed in which the location of post-response stimulation was manipulated within subjects. The results showed that: (1) the Simon effect can both decrease and increase in the presence of post-response stimuli, and (2) the amounts of Simon interference and Simon facilitation are both affected by post-response stimuli, whereas performance on neutral trials is not. These findings provide additional support for the action-concept view and suggest that further research concerning this new approach is warranted.     

Between-dimension flanker effects: A clarification with encouraging implications

Models of selective and divided attention have evolved to be remarkably similar (e.g., Cohen & Shoup, 1997; Mordkoff & Yantis, 1993). One remaining difference between these models is the inclusion of all-or-none gates within a recent model of selective attention; the existence of these gates is supported by the absence of a between-dimension flanker effect. However, the existence of these gates is also inconsistent with a recent model of divided attention. In the present experiment, the evidence in favor of all-or-none gates was explored, with the following result: When the task involves colors and letters as the stimuli, and when display features are presented at equal rates, no evidence of these gates is observed. Although other issues remain to be resolved, these findings bode well for the general goal of a unified model of divided and selective attention.     

Testing models of the redundant-signals effect: A warning concerning the combination-rule regression analysis

The redundant-signals effect is the observed RT advantage for trials presenting two or more targets, as compared with trials with only one target Two general classes of parallel-processing model have been proposed to explain this effect race models (e.g., Raab, 1962) and coactivation models (e.g., Miller, 1982). Various distributional analyses have been used in work aimed at discriminating between these two model classes. The present study reexamined one of these tests—the combination-rule regression analysis based on variable-criterion theory (Grice, Canham, & Boroughs, 1984)—by applying it to the data from two sets of simulated experiments. One set of simulations assumed coactivation; the other set assumed an independent race on redundant-target trials. Nearly identical combination-rule values were observed in the two sets of simulations. This finding shows that the combination rule of variable-criterion theory does not discriminate between models capable of explaining the redundant-signals effect The implications of this finding are briefly discussed     

Detecting conjunctions of color and form in parallel

Researchers have proposed that graphical efficacy may be determined, in part, by the nature of the perceptual interactions that exist between attributes used to create graphical displays. One extreme type of interaction isintegrality, in which two or more physical dimensions are represented as a single psychological dimension in the observer. An alternative type of interaction isconfigurality, in which a global emergent dimension is availableto the observer in addition to the component attributes. Thirteen stimulus sets, each composed of attributes commonly used in the design of graphs, were submitted to the performance-based diagnostics of integrality and configurality. Analyses suggest a continuum of configurality among the present stimulus sets, with little evidence for integral graphical attributes. The configural pattern of results was more common when two identical dimensions were paired (homogeneous stimuli) than when two different dimensions were paired (heterogeneous stimuli). However, there was no evidence that pairs of dimensions belonging to a single object (object integration) were any more configural than dimensions belonging to different objects. Object integration was, however, consistently related to inefficient performance in tasks requiring the filtering of one of two component dimensions.     

Dividing attention between color and shape revisited: redundant targets coactivate only when parts of the same perceptual object

When a single perceptual object provides two different reasons for a particular decision (by containing two qualitatively different targets), detailed analyses of the response-time distributions have shown that the two different reasons are jointly responsible for the final decision. The question is whether this coactivation occurs because the two targets contained by the object were from separate dimensions (e.g., color and shape) or were parts of the same perceptual object. Early work argued in favor of dimensions, implying that the types of information being processed is critical, as opposed to their sources; more recent work has argued in favor of objects. Experiment 1 in the present paper corrected for a potential bias in the design of some recent studies and found additional evidence in favor of objects. Two additional experiments directly manipulated whether redundant targets would be perceived as parts of one or two perceptual objects (while holding all else constant) and produced the strongest evidence to date that coactivation requires that the redundant targets be parts of one object. This reverses the original conclusion and suggests that the sources of information are critical, as opposed to the types. Two specific versions of the object-based model are discussed.     

Dividing attention between color and shape: Evidence of coactivation

When attention is divided between spatially distinct objects, the time-to detect a target decreases when two or more targets are present. This redundancy gain can be accounted for by an interactive race model (Mordkoff & Yantis, 1991) in which separate decisions are made about each object, but environmental contingencies among the objects can influence decision times. In the present study, we examined whether the model also accounts for performance when attention must be divided between stimulus attributes other than spatial location. Subjects made target-present responses when displays included a prespecified color, a prespecified letter, or both target features. The data violated the predictions of all separate-activations models, including the interactive race model. Two control experiments ruled out an alternative account based on task complexity. We conclude that coactivation occurs when target attributes from two separable dimensions are simultaneously present, but not when target attributes come from the same dimension. A modular hybrid of race and coactivation models is tentatively proposed.     

Redundancy gains and coactivation with two different targets: The problem of target preferences and the effects of display frequency

When a visual display contains two targets, both of which require the same response, reaction times (RTs) are faster than when only one target appears. This effect has previously been obtained regardless of whether the redundant targets are the same or different in shape, and in at least one set of two-target experiments, the redundancy gains have been larger for different targets (Grice & Reed, 1992). Experiments with two different targets have also revealed violations of the race-model inequality, suggesting that redundant targets coactivate the response (Miller, 1982). The present paper reexamines both of these findings, because both appear to be inconsistent with the interactive race model (Mordkoff & Yantis, 1991). Experiment 1 shows that the race-model inequality is not violated when the experimental design is free of biased contingencies; Experiment 1 also provides evidence that target preferences may artifactually produce the RT advantage fordifferent- oversame-target trials. Experiment 2, however, shows that the race-model inequality is violated when the frequencies of single- and redundant-target displays are equated (without introducing any biased contingencies), implying that the interactive race model cannot account for the results of experiments involving more than one type of target. Alternative loci for coactivation are briefly discussed.