George Houghton

Inhibition and Interference in Selective Attention: Some Tests of a Neural Network Model

We describe a neural network system that models selective action—that is, how an organism selectively responds to an object when other objects evoke competing responses. Performance of the model during simulations of various selective action situations reveals a number of interesting patterns of data. Specifically, the model shows a complex relationship between how much a distractor interferes with response to a target and how much inhibition is associated with the distractor. Subsequent experiments with human subjects reveal that the paradoxical behaviour of the model is also observed in human behaviour. We conclude that the similar performance characteristics of the model and human subjects in a variety of situations suggest that the model has captured some of the essential properties of mammalian selective action mechanisms.

NORMAL AND IMPAIRED SPELLING IN A CONNECTIONIST DUAL-ROUTE ARCHITECTURE

This paper presents a dual-route connectionist model of spelling, in which one route maps directly from sound to spelling (phonemes to graphemes), while in the other route the mapping is mediated by a further level of representation. The direct route is implemented as a two-layer associative network, with syllabically structured phonemic (input) and graphemic (output) representations, which comes to behave as a productive sound-to-spelling conversion mechanism through the exposure to a corpus of monosyllabic words. The mediated route is modelled as a frequency-sensitive lexical pathway. Nodes representing more frequent words become activated more rapidly than those of lower-frequency words. Access to both routes occurs in parallel, and the final spelling is determined by the combined output of both routes. We show that the model accounts for a wide range of data from normal spellers (including nonword spelling, the variability in vowel spelling and the effect of surrounding phonological context, frequency effect and its interaction with spelling regularity). We also investigate the effect of a selective lesion to the lexical route in which the ceiling of lexical activation is lowered. This manipulation produces a model with surface dysgraphic characteristics, which is tested against data from two impaired subjects. As well as simulating the classic surface dysgraphic profile, including a frequency by regularity interaction, the model exhibits a phenomenon that has only recently been reported, and which provides strong evidence for the idea that multiple routes are active in parallel, and combine to produce the final spelling.

The Role of Cue-Target Translation in Backward Inhibition of Attentional Set.

Backward inhibition (BI) refers to a reaction time cost incurred when returning to a recently abandoned task compared to returning to a task not recently performed. The effect has been proposed to reflect an inhibitory mechanism that aids transition from one task to another. The question arises as to precisely what aspects of a task may be inhibited and when the process takes place. Recent work has suggested a crucial role for response-related components of the task, which occur late in the typical trial structure (cue-target-response). In contrast to this suggestion, the authors present evidence that the way in which the task is cued can also modulate BI. Specifically, they find that the less transparent the cue-target relationship, the greater the level of BI. This also demonstrates that BI can be triggered at early stages of the trial structure, specifically during task preparation and prior to response processes. The authors conclude that BI is not tied to any particular component of the task structure but arises from whatever component generates the greatest intertrial conflict.

Semantic priming in the prime task effect: Evidence of automatic semantic processing of distractors

The automaticity of the semantic processing of words has been questioned because of the reduction of semantic priming when the prime word is processed nonsemantically—for example, in letter search (the prime task effect). In two experiments, prime distractor words produced semantic priming in a subsequent lexical decision task, but with the direction of priming (positive or negative) depending on the prime task. Lexico-semantic tasks produced negative semantic priming, whereas letter search produced positive semantic priming. These results are discussed in terms of task-based inhibition. We argue that, given the results from the distractors, the absence of semantic priming does not indicate an absence of semantic activation but reflects the action of control processes on prepotent responses when less practiced responses are needed.

Word-based grouping affects the prime-task effect on semantic priming

Semantic priming between words is reduced or eliminated if a low-level task such as letter search is performed on the prime word (the prime task effect), a finding used to question the automaticity of semantic processing of words. This idea is critically examined in 3 experiments with a new design that allows the search target to occur both inside and outside the prime word. The new design produces the prime task effect (Experiment 1) but shows semantic negative priming when the target letter occurs outside the prime word (Experiments 2 and 3). It is proposed that semantic activation and priming are dissociable and that inhibition and word-based grouping are responsible for reduction of semantic priming in the prime task effect.

Temporal cue–target overlap is not essential for backward inhibition in task switching

Lag 2 repetition costs are a performance cost observed when participants return to a task after just one intervening trial of a different task, compared to returning after a longer interval (AB A vs. CB A sequences, where A, B, C are tasks). This effect is known as backward inhibition (BI) and is thought to reflect the need to overcome inhibition applied specifically to Task “A” during disengagement at trial n – 1. Druey and Hübner (2007) have suggested that employment of such a specific inhibitory mechanism relies upon the cue and the target of the task overlapping temporally. We provide evidence across three experiments (including a direct replication attempt) that this is not the case, and that the presence of task-specific BI relies to some extent on the need to translate the cue–target relationship into working memory. Additionally, we provide evidence that faster responses in no overlap conditions are driven by low-level perceptual differences between target displays across overlap conditions. We conclude that BI is an effective sequential control mechanism, employed equally in cases of temporally overlapping and temporally separated cues and targets.

Heightened Conflict in Cue-Target Translation Increases Backward Inhibition in Set Switching.

Backward inhibition (BI) is a performance cost that occurs when an individual returns to a task after 1 (vs. more than 1) intervening trial, and it may reflect the inhibition of task-set components during switching. In 3 experiments, we support the theory that inhibition can target cue-based preparatory stages of a task. Participants performed a cued target-localization task that had been previously shown to produce BI. In Experiment 1, reassignment of arbitrary cue-target pairings midway through the experiment doubled the size of BI, though cue, target, and response sets remained unchanged. In Experiment 2, we controlled for effects of order of conditions or simple change of cue meaning. In Experiment 3, we demonstrated that the effect depends on re-pairing members of the same cue and target sets. The results are attributed to heightened conflict (and hence greater inhibition) during cue-target translation when a previously learned cue-target mapping is remapped.

On costs and benefits of n−2 repetitions in task switching: towards a behavioural marker of cognitive inhibition

Inhibition in task switching is inferred from slower reaction times returning to a recently performed task after one intervening trial (i.e. an ABA sequence) compared to returning to a task not recently performed (CBA sequence). These n−2 repetition costs are thought to reflect the persisting inhibition of a task after its disengagement. As such, the n−2 repetition cost is an attractive tool for the researcher interested in inhibitory functioning in clinical/neurological/neuroscience disciplines. In the literature, an absence of this cost is often interpreted as an absence of inhibition, an assumption with strong implications for researchers. The current paper argues that this is not necessarily an accurate interpretation, as an absence of inhibition should lead to an n−2 repetition benefit as a task’s activation level will prime performance. This argument is supported by three instances of a computational cognitive model varying the degree of inhibition present. An inhibition model fits human n−2 repetition costs well. Removal of the inhibition—the activation-only model—predicts an n−2 repetition benefit. For the model to produce a null n−2 repetition cost, small amounts of inhibition were required—the reduced-inhibition model. The authors also demonstrate that a lateral-inhibition locus of the n−2 repetition cost cannot account for observed human data. The authors conclude that a null n−2 repetition cost provides no evidence on its own for an absence of inhibition, and propose reporting of a significant n−2 repetition benefit to be the best evidence for a lack of inhibition. Implications for theories on task switching are discussed.

Attention and the control of action: An investigation of the effects of selection on population coding of hand and eye movement

The ecological approach to perception, particularly associated with Gibson [1], maintains that perception and action systems are closely linked and interactive. Perception cannot have evolved, as it were, for its own sake, but rather for its value in guiding the characteristic behaviours of particular organisms. This perspective predicts that perception-action couplings are not arbitrary, but that particular perceptual systems have evolved to be specially attuned or sensitive to particular types of information relevant for the triggering and control of particular responses, e.g., the fly-catching system in the frog [2]. Conversely actions can be produced to aid perception, a good example being the vestibulo-ocular reflex (VOR) which stabilizes retinal input when the head is moving, by automatically causing compensatory eye movements in the opposite direction.

Cue-switch costs in task-switching: cue priming or control processes?

In the explicitly cued task-switching paradigm, two cues per task allow separation of costs associated with switching cues from costs of switching tasks. Whilst task-switch costs have become controversial, cue-switch costs are robust. The processes that contribute to cue-switch costs are under-specified in the literature: they could reflect perceptual priming of cue properties, or priming of control processes that form relevant working memory (WM) representations of task demands. Across two experiments we manipulated cue-transparency in an attention-switching design to test the contrasting hypotheses of cue-switch costs, and show that such costs emerge from control processes of establishing relevant WM representations, rather than perceptual priming of the cue itself. When the cues were maximally transparent, cue-switch costs were eradicated. We discuss the results in terms of recent theories of cue encoding, and provide a formal definition of cue-transparency in switching designs and its relation to WM representations that guide task performance.