Kevin J. Hawley

Attention capture by novel stimuli

Abstract : In several experiments, observers were given glimpses of 4-word arrays. Accuracy of word location was tested after each array. Some words, called familiar, appeared many times across the series of arrays; others, called novel, appeared only once. The ratio of novel to familiar words in an array ranged from 0:4 to 4:0. When familiar and novel words were not intermixed (in 0:4 to 4:0 arrays), localization accuracy was higher for familiar words. However, when they were intermixed, especially in 1:3 arrays, accuracy tended to be higher for the novel words. This novel popout effect was the outcome of the suppressed localizability of the familiar words (relative to the 0:4 baseline) and the enhanced localizability of the novel words (relative to the 4:0 baseline). We attribute novel popout to the automatic orientation of attention away from more fluently unfolding regions of the perceptual field (familiar objects) and toward less fluently unfolding regions (novel objects).

Contribution of perceptual fluency to recognition judgments

Following a shallow (count vowels) or deep (read) study task, old and new words were tested for both fluency of perception and recognition memory. Subjects first identified a test word as it came gradually into view and then judged it as old or new. Old words were identified faster than new words, indicating implicit, perceptual memory for old words. Independently of this effect, words judged old were identified faster than words judged new, especially after shallow study. Eight experiments examined the possible causal relationship between perceptual fluency and recognition judgements. Experiments 1 to 4 showed that fast identifications per se do not promote old judgments. Accelerating the identification of test items by semantically priming them or making them come more quickly into view did not affect recognition judgments. Experiment 5 showed that the usual association of fast identifications with old judgments is not an artifact of item selection because the association disappeared when the identifications and judgements were segregated into different phases of the test task. Experiments 6 and 7 showed tha the likelihood of old judgments increases directly with the pretested perceptibility of test words, but only after shallow study. Experiment 8 showed that the dependency of recognition judgments on perceptual fluency continues to hold when the requirement to identify the words before judging them is eliminated. We conclude that fluency of perception contributes to recognition judgments, but only when the fluency is produced naturally (e.g., through perceptual memory) and explicit memory is minimal.

Perceptual inhibition of expected inputs: The key that opens closed minds.

The mind appears to be biased simultaneously toward both expected and unexpected inputs. For example, familiar scenes are usually perceived more readily than novel scenes, indicating the former bias, but a single novel object sometimes pops out from a familiar field, indicating the latter bias. A diverse literature and a computational model converge on the following resolution to this paradox: The former bias is conceptually driven and actually suppresses data-driven processing of expected inputs; in turn, this suppression disinhibits data-driven processing of unexpected inputs, yielding the latter bias. Evidence for suppressed data-driven processing of expected inputs is drawn from studies of perceptual habituation, semantic satiation, memory inhibition, inhibition of return, repetition blindness, primed inhibition, the word-inferiority effect, registration without learning, and both expert- and schema-based inhibitory effects. Evidence for enhanced data-driven processing of unexpected inputs is drawn from studies of the orienting response, mismatch negativity, memory facilitation, both expert- and schema-based facilitatory effects, and perceptual popout. The model, calledmismatch theory, incorporates inhibitory and facilitatory perceptual dynamics and is found to simulate the opposing biases. Implications of mismatch theory for perceptual phenomenology, dynamic systems theory, mental health, and individual differences are also discussed.

Long-term perceptual memory for briefly exposed words as a function of awareness and attention.

Two experiments investigated the possibility that perceptual memory for words is dependent on level of awareness of those words. In Experiment 1, subjects attempted to report briefly exposed words in a study phase and then identify words that faded into view in a test phase. Old words appeared in both the study and test phases, whereas new words appeared only in the test phase. Perceptual memory, indexed as the faster identification of old vs. new words, was observed only for words correctly reported in the study phase. In the study phase of Experiment 2, words were flanked by digits, and the distribution of attention between words and digits was varied. Perceptual memory increased from nil to high levels as more attention was allocated to the words. These findings suggest that long-term perceptual memory is dependent on level of awareness of words in the study phase.

Novel popout: empirical boundaries and tentative theory

Observers received glimpses of 4-word arrays and were probed for the locations of particular words. Familiar words were repeated across arrays but novel words were not. Accuracy was higher for familiar than for novel arrays, but this baseline difference was diminished when a single novel word appeared with three familiar words. In these arrays, accuracy rose above baseline for novel words, defining novel popout (NPO), and fell below baseline for familiar words, defining familiar sink-in (FSI). In Experiments 1-4, these effects increased directly with field familiarity and associative unitization. In Experiments (-e, NPO remained intact and FSI actually increased as duration of array exposure was reduced from 200 ms to as brief as 33 ms. At brief exposures, even familiar words popped out from fields in which they had never before appeared

Novel popout with nonsense strings: Effects of predictability of string length and spatial location

Recent studies have shown that when one of four expected words is replaced by a single unexpected word, the unexpected word may capture attention. In three experiments, we explored the generality of this effect. In each experiment, observers viewed arrays composed of four computergenerated “nonsense” strings. Accuracy of string localization was assessed after each array. Some strings, calledfamiliar, appeared in many arrays, whereas others, callednovel, appeared in only one. In each experiment, novel strings in arrays composed of one novel and three familiar strings were localized more accurately than were novel strings in arrays composed entirely of novel strings, and familiar strings in these arrays were localized less accurately than were familiar strings in arrays composed entirely of familiar strings. These two effects, termednovel popout andfamiliar sink-in, respectively, were observed even when novel and familiar strings were rendered less discriminable by holding their lengths constant (Experiment 2) and when familiar strings always appeared in the same spatial locations (Experiment 3). The data suggest that novel objects can capture attention even when the objects lack any clear linguistic referent, when they are superficially similar to the familiar objects that surround them, and when the spatial locations of familiar objects are completely predictable.

PsyExper: Another experimental generation system for the IBM PC

A system for creating and running psychological experiments on IBM PC compatible computers is described. The system attempts to reconcile the demand for flexible and powerful experimental software with the need for systems that are easy to understand and modify. Experiments are created by building a series of displays with variable compositions, durations, and stimulus onset asynchronies. The number, type, location, color, and perceptibility of stimuli within these displays can be systematically varied. Reaction time and other response measures can be collected from the keyboard, a voice-activated switch, or other external switches. The system is assembled from a series of Turbo Pascal and Turbo C routines that may be modified by the user or incorporated into new routines. Custom modules can be added easily to any of the system’s menus. The system is best suited for discrete trial experiments with target detection, perceptual priming, lexical decision, or recognition memory tasks.

An inexpensive sound-activated switch for experiments measuring vocal-response times

An inexpensive sound-activated switch suitable for experiments measuring vocal-response times is described. This switch is comparable to many commercially produced switches in terms of its control over input sensitivity and response delay times, but it can be assembled for a fraction of the cost. Additionally, the present switch provides many features not found on standard commercial models such as a built-in speaker for monitoring the input signal and output jacks to facilitate simultaneous recording of this signal. Reliability estimates suggest that performance for this switch is comparable to that of a Scientific Prototype Model 761-G when both units are equated for frequency sensitivity and response delay time. In all, this switch offers a reliable and practical alternative to commercially produced devices for experiments in which the onset of an auditory signal must be accurately detected.

Independent control of dual video subsystems on the IBM PC and compatibles

Two methods for generating video output on multiple video monitors are described. The first method involves splitting the signal from a single video adaptor card-so that multiple video monitors may be attached. Although this method is simple and relatively cost-effective, it is limited to adaptors that produce only digital video signals, thus precluding the use of VGA systems and composite displays. The second method involves the installation and programming of video adaptors: Two sample programs, which control a secondary adaptor by means of either BIOS routines or direct commands via C code, are described. Although more complex, this second method allows output to each display to be controlled independently. Furthermore, output to one screen may consist of graphics information while output to the second screen consists of text. Together, both methods can be used to create an experimental system composed of multiple data-collection stations and an independent experimenter console.