Chris M. Herdman

Attentional modulation of visual processes in motion perception.

The present research examined the effects of spatially directed attention on the temporal characteristics of information transmission in the visual system. A two-stimulus, two-flash, long-range motion display was used. The results showed that attending to 1 of the 2 stimuli altered the perceived direction of motion, the pattern of motion and no-motion responses, and ratings of motion quality. The results were compared with predictions derived from 2 conceptual frameworks of attention: a temporal-profile model and an additive account. The results supported the temporal-profile model

Attentional resource demands of visual word recognition in naming and lexical decisions

Attentional demands of lexical access were assessed with dual-task methodology. Subjects performed an auditory probe task alone (single-task) or combined (dual-task) with either a lexical decision or a naming task. In Experiment 1, probe performance showed a decrement from single- to dual-task conditions during recognition of words in both lexical decision and naming tasks. In addition, decrements in probe performance were larger during processing of low-frequency compared with high-frequency words in both of the word recognition tasks. Experiment 2 showed that the time course of frequency-sensitive demands was similar across lexical decision and naming tasks and that attention is required early in the word recognition sequence. The results support the assumption that lexical access is both frequency sensitive and attention demanding.

Naming cAsE aLtErNaTeD words

A dual-route approach was used as an initial framework to examine the relation between presentation format and lexical processing in a naming task. In Experiments 1 and 3, words were presented in lowercase versus case-alternated format. Presentation format interacted with word frequency and regularity: For irregular words (e.g.,pint), case alternation was additive with frequency, whereas for regular words (e.g.,mint), case alternation and frequency interacted. Experiment 2 dissociated the locus of case-alternation effects from those of stimulus intensity. Stimulus intensity was additive with frequency and regularity, suggesting that whereas stimulus intensity affects encoding, case alternation affects lexical processing at a postencoding stage in the word recognition system. It was concluded that a dualroute approach provides a suggestive but incomplete account of how case alternation influences lexical processing. As an alternative to a dual-route approach, we show that the present results can be addressed and successfully simulated using an implemented version of Norris’s (1994) multilevel model.

Disruptive camouflage impairs object recognition

Whether hiding from predators, or avoiding battlefield casualties, camouflage is widely employed to prevent detection. Disruptive coloration is a seemingly well-known camouflage mechanism proposed to function by breaking up an objects salient features (for example their characteristic outline), rendering objects more difficult to recognize. However, while a wide range of animals are thought to evade detection using disruptive patterns, there is no direct experimental evidence that disruptive coloration impairs recognition. Using humans searching for computer-generated moth targets, we demonstrate that the number of edge-intersecting patches on a target reduces the likelihood of it being detected, even at the expense of reduced background matching. Crucially, eye-tracking data show that targets with more edge-intersecting patches were looked at for longer periods prior to attack, and passed-over more frequently during search tasks. We therefore show directly that edge patches enhance survivorship by impairing recognition, confirming that disruptive coloration is a distinct camouflage strategy, not simply an artefact of background matching.

The Role of Working Memory in Supporting Drivers’ Situation Awareness for Surrounding Traffic

Objective: To link working memory to driver situational awareness (SA) for surrounding traffic. Background: Operating a motor vehicle is a complex activity that requires drivers to maintain a high level of SA. Working memory has been conceptually linked to SA; however, the roles of working memory subsystems in supporting driver SA is unclear. Method: Participants drove a simulated vehicle and monitored surrounding traffic while concurrently performing either visuospatial- or phonological-load tasks. Drivers’ SA was indexed as the ability to recall the positions of the surrounding traffic relative to their own vehicle at the end of each trial. Results: In Experiment 1, a visuospatial task interfered with drivers’ ability to recall the positions of traffic located in front of their vehicle. In contrast, a phonological task interfered with drivers’ ability to recall the positions of traffic located behind their vehicle. Experiment 2 confirmed and extended the findings of Experiment 1 with the use of different visuospatial- and phonological-load tasks. Conclusion: Visuospatial and phonological codes play a role in supporting driver SA for traffic located in the forward view and the rear view, respectively. Application: Drivers’ SA for surrounding vehicles is disrupted by concurrent performance on secondary tasks. The development and implementation of new in-cabin communication, navigation, and informational technologies needs to be done with the knowledge that components of drivers’ working memory capacity may be exceeded, thereby compromising driving safety.

Base word Frequency and Pseudohomophone Naming

The advantage of naming pseudohomophones over non-pseudohomophones has been interpreted as reflecting the contribution of whole-word lexical representations in phonological coding. A whole-word interpretation was further supported by Taft and Russell (1992), who reported a pseudohomophone frequency effect such that pseudohomophones were named faster if they corresponded to high- than to low-frequency base-words (e.g. poast vs. hoast). Experiment 1 replicated this pseudohomophone frequency effect using the Taft and Russell items. Further analyses showed, however, that the pseudohomophones in Taft and Russells high-frequency group were more orthographically similar to words than the pseudohomophones in the low-frequency group. These differences in orthography may have been the cause of the “frequency” effects. In Experiment 2, a new set of high- and low-frequency pseudohomophones was constructed that were matched on orthographic factors (i.e. SPBF and N). With these items, a standard pseudohomophone advantage was found such that pseudohomophones were named faster and more accurately than non-pseudohomophones. However, in contrast to Taft and Russells results, pseudohomophone naming was not related to base-word frequency. We conclude that the pseudohomophone advantage occurs at a postlexical stage in non-word naming.

Implicating the lexicon: Base-word frequency effects in pseudohomophone naming.

Ss named pseudohomophones (e.g., phocks) and nonpseudohomophones (e.g., snack) under conditions in which words were or were not included in the stimulus lists. For Ss classified as fast responders, pseudohomophone advantages were not accompanied with base-word frequency effects. For slow responders, pseudohomophone naming was related to base-word frequency, but only when words were included in the stimulus lists. A dual-route model is proposed in which (a) lexical representations are frequency sensitive, (b) the relative use of nonlexical vs. lexical information in phonological synthesis depends on strategic factors, and (c) overlapping lexical and nonlexical codes are assumed to lengthen processing time at the level of a phonological buffer

Effects of Conversation on Situation Awareness and Working Memory in Simulated Driving

Objective: In the present research, we investigated the hypothesis that working memory mediates conversation-induced impairment of situation awareness (SA) while driving. Background: Although there is empirical evidence that conversation impairs driving performance, the cognitive mechanisms that mediate this relationship remain underspecified. Researchers have reported that a phonological working memory task decreased drivers’ SA for vehicles located behind them whereas a visuospatial working memory task impaired SA for vehicles ahead. Conversation, therefore, might impair SA for vehicles behind the driver by preferentially taxing the phonological loop. Method: A 20-questions task was used as a proxy for natural conversation. In Experiment 1, driving performance was measured across three within-subjects conversation conditions (i.e., no conversation, driver asks questions, driver answers questions) with the use of a driving simulator. In Experiment 2, participants drove in the same simulator while either conversing (20-questions task) or not. Participants estimated the positions of other vehicles after the screens were blanked at the end of each trial. Results: Speed monitoring and responses to visual probes were impaired by the 20-questions conversation task (Experiment 1). As predicted, conversation impaired SA for the location of other vehicles more for vehicles located behind the driver than for those in front (Experiment 2). Conclusion: Conversation impairs drivers’ SA of vehicles behind them by taxing working memory’s phonological loop and impairs SA generally by taxing working memory’s central executive. Application: Provides a theoretical framework that links driver SA to working memory and a mechanism for understanding why conversation impairs driving performance.

Individual differences in the efficiency of word recognition

The purpose of this study was to examine the hypothesis that the attentional demands of word recognition covary with other measures of reading efficiency. Individual differences in efficiency were indexed by (a) speed and accuracy of lexical access, (b) obligatory activation of phonological codes, and (c) working memory capacity. The attentional demands of word recognition were measured with a dual-task technique. Subjects performed naming and probe-detection tasks separately (single task) and in combination (dual task). The results showed that single-task to dual-task decrements in performance on the naming and probe tasks were predicted by measures of the speed and accuracy of lexical access, obligatory activation of phonological codes, and efficiency of working memory. These findings provide support for the widespread assumption that the attentional demands of basic reading processes are a source of individual differences in reading skill.

Object-based attention and cognitive tunneling.

Simulator-based research has shown that pilots cognitively tunnel their attention on head-up displays (HUDs). Cognitive tunneling has been linked to object-based visual attention on the assumption that HUD symbology is perceptually grouped into an object that is perceived and attended separately from the external scene. The present research strengthens the link between cognitive tunneling and object-based attention by showing that (a) elements of a visual display that share a common fate are grouped into a perceptual object and that this grouping is sufficient to sustain object-based attention, (b) object-based attention and thereby cognitive tunneling is affected by strategic focusing of attention, and (c) object-based attention is primarily inhibitory in nature.