Heike Elchlepp

Proactive inhibitory control: a general biasing account

Highlights • Most work on proactive inhibitory control (PIC) is descriptive.• The theoretical accounts focus primarily on response- or motor-related processes.• We show that PIC biases stimulus detection and response selection.• We also demonstrate an overlap between various forms of proactive control.• Based on our findings, we propose a general biasing account for PIC.

A brain‐potential study of preparation for and execution of a task‐switch with stimuli that afford only the relevant task

Behavioural and neurophysiological studies of task‐switching have tended to employ ‘bivalent’ stimuli (which afford responses in two tasks). Using brain potential recordings, we investigated task‐switching with ‘univalent’ stimuli affording responses in only one of the tasks, and compared the outcomes to those recently obtained with bivalent stimuli (Lavric et al. [ 2008 ]: Eur J Neurosci 1‐14), in order to examine two phenomena. First, when only univalent stimuli are presented, the processing of task cues becomes optional. Our results showed that in these circumstances linguistic (but not pictorial) cues were still effective in eliciting at least some degree of preparation for a task‐switch, as evidenced by the reduction in the error cost of switching at the longer preparation interval and by a posterior switch‐induced ERP positivity at about 450–800 ms in the cue‐stimulus interval. Second, single affordance stimuli not only reduced behavioural switch costs relative to bivalent stimuli; they also produced a smaller post‐stimulus switch‐induced negativity, consistent with the latter being a marker of conflict between task‐sets. However, using stimuli not associated with responses in the alternative task did not completely eliminate the negativity. We speculate that the residue reflects other sources of conflict: attention to the irrelevant perceptual dimension and/or persistence of task goals. Hum Brain Mapp, 2011.

Perceptual Learning and Inversion Effects: Recognition of Prototype-Defined Familiar Checkerboards

The face inversion effect is a defection in performance in recognizing inverted faces compared with faces presented in their usual upright orientation typically believed to be specific for facial stimuli. McLaren (1997) was able to demonstrate that (a) an inversion effect could be obtained with exemplars drawn from a familiar category, such that upright exemplars were better discriminated than inverted exemplars; and (b) that the inversion effect required that the familiar category be prototype-defined. In this article, we replicate and extend these findings. We show that the inversion effect can be obtained in a standard old/new recognition memory paradigm, demonstrate that it is contingent on familiarization with a prototype-defined category, and establish that the effect is made up of two components. We confirm the advantage for upright exemplars drawn from a familiar, prototype-defined category, and show that there is a disadvantage for inverted exemplars drawn from this category relative to suitable controls. We also provide evidence that there is an N170 event-related potential signature for this effect. These results allow us to integrate a theory of perceptual learning originally proposed by McLaren, Kaye, and Mackintosh (1989) with explanations of the face inversion effect, first reported by Yin.

A brain‐potential correlate of task‐set conflict

Brain-potential correlates of response conflict are well documented, but those of task conflict are not. Task-switching studies have suggested a plausible correlate of task conflict--a poststimulus posterior negativity--however, in such paradigms the negativity may also reflect poststimulus task-set reconfiguration postulated in some models. Here, participants alternated between single-task blocks of classifying letters and digits; hence, no within-block task-set reconfiguration was required. Presenting letters alongside digits slowed responses to the digits and elicited an ERP negativity from ≈ 350 ms, relative to task-neutral symbols presented alongside digits, consistent with task conflict. The negativity was also present for congruent digit-letter stimuli; this and the lack of behavioral response congruency effects indicate conflict at the level of task-set rather than response selection.

Processing Differences Across Regular and Irregular Inflections Revealed Through ERPs

Research strongly suggests that printed words are recognized in terms of their constituent morphemes, but researchers have tended to consider the recognition of derivations and inflections in separate theoretical debates. Recently, Crepaldi et al. (2010) proposed a theory that claims to account for the recognition of both derivations and inflections. We investigated brain potentials in the context of masked priming to test 2 key predictions of this theory: (a) that regular inflections should prime their stems to a greater degree than irregular inflections should prime their stems and (b) that priming for regular inflections should arise earlier in the recognition process than priming for irregular inflections. Significant masked priming effects were observed for both regular and irregular inflections, though these effects were greater for regular inflections. ERP data further suggested that masked priming effects for regular and irregular inflections had different time courses. Priming for regular but not irregular inflections emerged in a time window reflecting processing up to 250 ms post target onset, and although priming for regular and irregular inflections was observed in a time window reflecting processing 400 to 600 ms post target onset, these effects arose earlier and were of greater magnitude for the regular inflections. These findings support a form-then-meaning characterization of the visual word processing system such as that proposed by Crepaldi et al. (2010) and raise challenges for alternative approaches.

Shifting attention between visual dimensions as a source of switch costs

Task-switching experiments have documented a puzzling phenomenon: Advance warning of the switch reduces but does not eliminate the switch cost. Theoretical accounts have posited that the residual switch cost arises when one selects the relevant stimulus–response mapping, leaving earlier perceptual processes unaffected. We put this assumption to the test by seeking electrophysiological markers of encoding a perceptual dimension. Participants categorized a colored letter as a vowel or consonant or its color as “warm” or “cold.” Orthogonally to the color manipulation, some colors were eight times more frequent than others, and the letters were in upper- or lowercase. Color frequency modulated the electroencephalogram amplitude at around 150 ms when participants repeated the color-classification task. When participants switched from the letter task to the color task, this effect was significantly delayed. Thus, even when prepared for, a task switch delays or prolongs encoding of the relevant perceptual dimension.

The effect of scrambling upright and inverted faces on the N170

The face inversion effect refers to a decrement in performance when we try to recognise familiar faces turned upside down (inverted), compared with familiar faces presented in their usual (upright) orientation. Recently, we have demonstrated that the inversion effect can also be found with checkerboards drawn from prototype-defined categories when the participants have been trained with these categories, suggesting that factors such as expertise and the relationships between stimulus features may be important determinants of this effect. We also demonstrated that the typical inversion effect on the N170 seen with faces is found with checkerboards, suggesting that modulation of the N170 is a marker for disruption in the use of configural information. In the present experiment, we first demonstrate that our scrambling technique greatly reduces the inversion effect in faces. Following this, we used Event-Related Potentials (ERPs) recorded while participants performed an Old/New recognition study on normal and scrambled faces presented in both upright and inverted orientations to investigate the impact of scrambling on the N170. We obtained the standard robust inversion effect for normal faces: The N170 was both larger and delayed for normal inverted faces as compared with normal upright faces, whereas a significantly reduced inversion effect was recorded for scrambled faces. These results show that the inversion effect on the N170 is greater for normal compared with scrambled faces, and we interpret the smaller effect for scrambled faces as being due to the reduction in expertise for those faces consequent on scrambling.