An optimal adjustment procedure to minimize experiment time in decisions with multiple alternatives

Decisions between multiple alternatives typically conform to Hick’s Law: Mean response time increases log-linearly with the number of choice alternatives. We recently demonstrated context effects in Hick’s Law, showing that patterns of response latency and choice accuracy were different for easy versus difficult blocks. The context effect explained previously observed discrepancies in error rate data and provided a new challenge for theoretical accounts of multialternative choice. In the present article, we propose a novel approach to modeling context effects that can be applied to any account that models the speed–accuracy trade-off. The core element of the approach is “optimality” in the way an experimental participant might define it: minimizing the total time spent in the experiment, without making too many errors. We show how this approach can be included in an existing Bayesian model of choice and highlight its ability to fit previous data as well as to predict novel empirical context effects. The model is shown to provide better quantitative fits than a more flexible heuristic account.     

The dynamics of choice among multiple alternatives

We consider neurally based models for decision-making in the presence of noisy incoming data. The two-alternative forced-choice task has been extensively studied, and in that case it is known that mutually inhibited leaky integrators in which leakage and inhibition balance can closely approximate a drift-diffusion process that is the continuum limit of the optimal sequential probability ratio test (SPRT). Here we study the performance of neural integrators in n?2 alternative choice tasks and relate them to a multihypothesis sequential probability ratio test (MSPRT) that is asymptotically optimal in the limit of vanishing error rates. While a simple race model can implement this ‘max-vs-next’ MSPRT, it requires an additional computational layer, while absolute threshold crossing tests do not require such a layer. Race models with absolute thresholds perform relatively poorly, but we show that a balanced leaky accumulator model with an absolute crossing criterion can approximate a ‘max-vs-ave’ test that is intermediate in performance between the absolute and max-vs-next tests. We consider free and fixed time response protocols, and show that the resulting mean reaction times under the former and decision times for fixed accuracy under the latter obey versions of Hick's law in the low error rate range, and we interpret this in terms of information gained. Specifically, we derive relationships of the forms log(n-1), log(n), or log(n+1) depending on error rates, signal-to-noise ratio, and the test itself. We focus on linearized models, but also consider nonlinear effects of neural activities (firing rates) that are bounded below and show how they modify Hick's law.     

The influence of the number of alternatives on the perceptual recognition threshold

A study of the recognition thresholds for nonsense syllables previously presented in lists containing from 2 to 15 syllables is reported. The threshold is found to increase in proportion to the logarithm of the number of alternatives (i.e. the length of the list from which a given test syllable is drawn). It is therefore concluded that recognition threshold is a function of the amount of information transmitted.     

Visual search for schematic emotional faces risks perceptual confound

Several studies have used a visual search task to demonstrate that schematic negative-face targets are found faster and/or more efficiently than positive ones, with these findings taken as evidence that negative emotional expression is capable of guiding attentional allocation in visual search. A common hypothesis is that these effects should be disrupted by face inversion; however, this has not been consistently demonstrated, and raises the possibility of a perceptual confound. One candidate confound is the feature of "closure" (see Wolfe & Horowitz, 2004) caused by the down-turned mouth adjacent to edge of the face. This was investigated in the present series of experiments. In Experiment 1, the speed advantage for upright negative faces was replicated. In Experiment 2, the effect was not disrupted with inversion, and an efficiency advantage emerged, suggesting that perceptual features could be causing the advantage. In Experiment 3, speed and efficiency effects were seen when this perceptual characteristic remained but face features were scrambled. Taken together, these findings suggest that visual search using schematic faces containing a curved-line mouth feature cannot provide a valid test of guided search by negative facial emotion unless this confound is controlled.     

A search for perceptual differentiation produced by nondifferential reinforcement

In each of four experiments (three using pigeons as the subjects and one using rats) animals in an experimental condition were given exposure to a pair of stimuli that subsequently they were required to discriminate between. During the exposure phase response to either stimulus was consistently followed by reward. These subjects were uniformly found to be retarded in learning the discrimination when compared with control subjects that received equivalent pre-training in the absence of the critical stimuli. These results provide no support for the suggestion that stimuli may become “perceptually differentiated” during the pre-training phase but are consistent with the proposal that novel stimuli possess a high level of associability that declines as a result of experience.     

Cuing interacts with perceptual load in visual search

We tested the strong form of the perceptual-load hypothesis, which posits that the amount of perceptual load is the only factor determining whether attention can be effectively focused. Participants performed a visual search task under conditions of low and high load and with either a 100% valid spatial cue or no spatial cue. With no cue, participants showed evidence of processing to-be-ignored stimuli when perceptual load was low but not when it was high, consistent with the perceptual-load hypothesis. However, with a 100% valid spatial cue, participants showed little evidence of processing to-be-ignored stimuli, even when perceptual load was low. These results suggest that although perceptual load may be an important factor in attentional selectivity, load alone is not sufficient to explain how and when selective attention is effective.     

Task-dependent sensitisation of perceptual and semantic processing during visual search for words

Two experiments examined the impact of task-set on people's use of the visual and semantic features of words during visual search. Participants' eye movements were recorded while the distractor words were manipulated. In both experiments, the target word was either given literally (literal task) or defined by a semantic clue (categorical task). According to Kiefer and Martens, participants should preferentially use either the visual or semantic features of words depending on their relevance for the task. This assumption was partially supported. As expected, orthographic neighbours of the target word attracted participants' attention more and took longer to reject, once fixated, during the literal task. Conversely, semantic associates of the target word took longer to reject during the categorical task. However, they did not attract participants' attention more than in the literal task. This unexpected finding is discussed in relation to the processing of words in the peripheral visual field.     

The optimal number of alternatives at a choice point with travel time considered

The problem of optimal design is considered for tasks that can be represented as n choice points with a_i alternatives per choice point. Examples are mazes or multiple choice tests. Some fixed time t′ elapses between choice points, say traveling from one to the other or reading a question, and additional time t is spent considering each alternative at the choice point. For fixed total time, the goal is to find the optimum number of choice points and the optimum number of alternatives at each choice point. In general, the longer the time spent between choice points, the greater the optimum number of alternatives at each point.     

Non-parametric inference for ordered alternatives in a randomized block design

This paper treats the problem of testing an ordered hypothesis based on the ranks of the data. The statistical procedures for the randomized block design with more than one observation per cell are derived. Multiple comparisons and estimation procedures are also included.     

The contents of perceptual hypotheses: Evidence from rapid resumption of interrupted visual search

Observers can resume a previously interrupted visual search trial significantly more quickly than they can start a new search trial (Lleras, Rensink, & Enns, 2005). This rapid resumption of search is possible because evidence accumulated during the previous exposure, a perceptual hypothesis, can carry over to a subsequent presentation. We present four interrupted visual search experiments in which the content of the perceptual hypotheses used during visual search trials was characterized. These experiments suggest that prior to explicit target identification, observers have accumulated evidence about the locations, but not the identities, of local, task-relevant distractors, as well as preliminary evidence for the identity of the target. Our results characterize the content of perceptual search hypotheses and highlight the utility of interrupted search for studying online search processing prior to target identification.     

The effect of learning condition on perceptual anticipation, awareness, and visual search

The efficacy of explicit and implicit learning paradigms was examined during the very early stages of learning the perceptual-motor anticipation task of predicting ball direction from temporally occluded footage of soccer penalty kicks. In addition, the effect of instructional condition on point-of-gaze during learning was examined. A significant improvement in horizontal prediction accuracy was observed in the explicit learning group; however, similar improvement was evident in a placebo group who watched footage of soccer matches. Only the explicit learning intervention resulted in changes in eye movement behaviour and increased awareness of relevant postural cues. Results are discussed in terms of methodological and practical issues regarding the employment of implicit perceptual training interventions.     

In search of perceptual priming in a semantic classification task

Four experiments tested for perceptual priming for written words in a semantic categorization task. Repetition priming was obtained for low-frequency words when unrelated categorizations were performed at study and test (Experiment 1), but it was not orthographically mediated given that written-to-written and spoken-to-written word priming was equivalent (Experiments 2 and 3). Furthermore, no priming was obtained between pictures and words (Experiment 4), suggesting that the nonorthographic priming was largely phonological rather than semantic. These results pose a challenge to standard perceptual theories of priming that should expect orthographic priming when words are presented in a visual format at study and test.     

Attention in visual search: multiple search classes.

Data from visual-search tasks are typically interpreted to mean that searching for targets defined by feature differences does not require attention and thus can be performed in parallel, whereas searching for other targets requires serial allocation of attention. The question addressed here was whether a parallel-serial dichotomy would be obtained if data were collected using a variety of targets representing each of several kinds of defining features. Data analyses included several computations in addition to search rate: (1) target-absent to target-present slope ratios; (2) two separate data transformations to control for errors; (3) minimum reaction time; and (4) slopes of standard deviation as a function of set size. Some targets showed strongly parallel or strongly serial search, but there was evidence for several intermediate search classes. Sometimes, for a given target-distractor pair, the results depended strongly on which character was the target and which was the distractor. Implications from theories of visual search are discussed.     

The multiple baseline design across exemplars

Three variations of the multiple baseline design (MBD) have been identified in the behavioral literature: MBD across behaviors, subjects and situations. This analysis proposes an important variant of the MBD across behaviors, namely the MBD across exemplars. In this variant, two or more components (exemplars) of the behavior class form the baselines of the design. Thus, intervention is applied separately and sequentially to each target exemplar. The implicit rule of the MBD across exemplars can be seen in several published papers in the behavioral literature. The value of recognizing this variant of the MBD across behaviors is its usefulness as an alternative experimental intervention in clinical settings where the possibility of a convincing research design might not otherwise be seen.     

In search of perceptual influences of sentence context on word recognition

A major issue in the study of word perception concerns the nature (perceptual or nonperceptual) of sentence context effects. The authors compared effects of legal, word replacement, nonword replacement, and transposed contexts on target word performance using the Reicher-Wheeler task to suppress nonperceptual influences of contextual and lexical constraint. Experiment 1 showed superior target word performance for legal (e.g., "it began to flap/flop") over all other contexts and for transposed over word replacement and nonword replacement contexts. Experiment 2 replicated these findings with higher constraint contexts (e.g., "the cellar is dark/dank") and Experiment 3 showed that strong constraint contexts improved performance for congruent (e.g., "born to be wild") but not incongruent (e.g., mild) target words. These findings support the view that the very perception of words can be enhanced when words are presented in legal sentence contexts.