7.2 Contributions of our work
7.2.4 A process-based approach to the attentional blink
With a view to studying the sequence of cognitive processes underlying the attentional blink and its modulation by emotion, we examined the AB curve through a novel methodology allowing the discretization of specific aspects of the data (Cousineau et al., 2006). In particular, this approach disentangles moments of interest, and provides non-biased measurements of its modulation by targets. In other words, it locates moments during the natural course of the AB that may reveal the occurrence of particular cognitive processes. To our knowledge, this is the first time that such an approach is being used to investigate the sequence of cognitive processes underlying the modulation of attentional blink (Chapter 5 on page 69), after the approach has been originally demonstrated.
Current models accounting for the attentional blink generally describe a two-stage process. Au-thors propose different interpretations of the underlying processing, often in relation to other hypothesised psychological phenomena (e.g. WM consolidation, “token” individuation), based on their subjective understanding of what may be happening and the results of their empirical work.
Cousineau et al. (2006) took a radically different direction by objectively describing the AB curve, capturing “aspects of the data that are most likely to be of theoretical importance” (p. 176) while remaining a-theoretical in nature, that is unbiased by a particular theory or model of the AB.
Each of these aspects may relate to particular aspects of the processing that may be sensitive in their own way to the material being presented. In particular, this approach distinguishes Lag-1 sparing differences, amplitude differences, width differences, and minimum accuracy differences.
Guiding the interpretation of our results by means of emotion theories allowed us to formulate new hypotheses as to the function and the nature of the processes illustrated by the AB effect. We observed three different periods of time (Figure 7.1), which are differently sensitive to emotional information (Section 7.2.2 and 7.2.3). These periods of time may see the unfolding of several processes implementing different functions.
Figure 7.1: Proposed scenario accounting for the AB effect. Following the onset of the first target (T1), we identify three periods differently sensitive to emotional information. Each period may see the computation of a number of processes implementing particular functions.
We hypothesise that the overall aim of this sequence is a) to prioritise the processing of the first target, b) to prevent intrusions, and c) to keep some order in the processing flow.
(Original work elaborated in the course of this thesis.)
We propose the following scenario, generally hypothesising the implications of two features of the cognitive system: preemptive signalling and information integration. Both have already been addressed in the context of the attentional blink separately (Section 2.2 on page 26, for a review).
We propose that they are both involved at some level with what is being observed through the AB curve, through different timing, and attempt to phrase the unfolding of the processing as follows.
Preemptive signalling. This part of the scenario is inspired by a theoretical paradigm in computer science called preemptive multi-tasking (Tanenbaum & Woodhull, 2006), which aims at ordering the tasks performed by computers, ensuring that all processes get some amount of central processing time at any given time. Nowadays, it is implemented by most operating systems as a way of emulating parallel processing on otherwise serial processors (CPU). It generally involves the use of an interrupt mechanism that both invokes a scheduler to determine which process should be next executed, and suspends any other executing process by emitting a preemptive signal.
We propose that similar mechanisms may account for the ignition of the attentional blink. The first period of time we observed (Figure 7.1, Period A) starts on the onset of the first target, and finishes during the onset of the “blink” mechanism. We hypothesise that this mechanism is a ballistic reaction to the perception of the first target, aiming at supporting its processing while preventing intrusion, in a similar way as preemptive signals emitted in today’s operating systems.
We hypothesise that this mechanism is implemented in the locus coeruleus–norepinephrine system (LC–NE), which has been implicated in the ignition and maintenance of arousal states and already hypothesised as a factor in the attentional blink (see Section 2.2.4 on page 32).
This first period of time is often referred to as the “lag-1 sparing” because, under certain conditions, both targets seem to be able to access subsequent levels of processing. However, activated repre-sentations are not immune to interference. As we have shown in our experiments and reported by others (e.g., Dehaene et al., 2003; Hommel & Akyurek, 2005), the report of the first target can be prevented by the second target. During that period of time, the “blink” mechanism slowly unfolds, preventing the processing of the second target altogether. The second period of time (Figure 7.1, Period B) constitutes the peak of this interference. We did not find that the amount of “blink” was modulated by emotion, thus we hypothesise that this ballistic process occurs in an all-or-nothing manner.
Information integration. We generally hypothesise that the peak of the AB (Figure 7.1, Period B) would signal the peak of information integration yielding conscious awareness and correct
identification. As reviewed earlier (Section 2.2 on page 26), several authors hypothesised that the core of this stage of processing involves the invocation of some kind of a global workspace (GW) that would integrate all information available about the task and the target10. Evidence indeed suggests that no later than 300 msec after the onset of the first target, a distributed, target-dedicated and task-related network of temporo-parietal-frontal network shows coupling behaviour through phase synchrony (e.g., Gross et al., 2004; Sergent et al., 2005; Hommel et al., 2006).
The concept of GW refers to the notion that the different high-level, specialised, brain areas involved in the processing of (visual) stimuli interconnect to each other (Baars, 1988, 2002; Baars
& Franklin, 2003), to form a global workspace processing the stimuli into a unitary assembly supporting conscious reportability. Perceived stimuli would thus compete to recruit this global workspace that, once activated, only affords exclusive access, yielding to the inability to process subsequent stimuli for a transient period of time (Figure 7.1, Period B).
In particular, Hommel et al. (2006) hypothesise that after nonselective processing in specialised perceptual cortices, targets are fed to object-specific temporal areas, where they are matched against long-term knowledge and, consequently, identified. Identified objects are then maintained in frontal working memory, and receive support by means of the synchronisation of the relevant structures in frontal and parietal cortices. Seemingly closing a perceptual window, this synchroni-sation stabilises the representation maintained in working memory, increasing the likelihood that the target be reported, and preventing other stimuli from entering further processing. The general availability of the cognitive system is then slowly restored (Figure 7.1, Period C).
In our scenario, both preemptive signalling and information integration are only hypothesised featuresof the information processing system, which can only be “perceived” through appropriate methods, tools and experimental paradigms. The reader should therefore avoid visualising yet another couple of dedicated modules grounding the implementation of these features in the brain.
They are most likely separable although interacting, and most likely involve many more complex processing steps than foreseen by this naive scenario.
Guiding our investigation through the lenses of emotion theories provides nonetheless some light on potential implementations in the brain, and might partly explain why emotion-laden stimuli seem to benefit from a heightened processing priority. The amygdala for instance, is in the highlight of most emotion theories. It is known to be crucial in fear processing and fear learning (Vuilleumier, 2005), and a growing body of data also seems to suggest that the scope of its functional domain generally spans information that isrelevant for the individual’s general well-being (Sander et al.,
2003). Its position in the processing stream of perceptual information makes it a perfect candidate to potentially influence many cortical and subcortical regions. If there is still some debate about the precise circuitry involving the amygdala in humans, researchers agree nonetheless to attribute an initial appraisal of emotional significance to this brain structure, based on coarse and limited information, early in the processing stream. This influence could take the form of direct feedback to sensory cortices (Vuilleumier, 2005), but also as indirect modulation of parietal and frontal regions (e.g., PFC) through the LC–NE system. These top-down influences would then produce a cascade of events which would signal emotional significance, which could be modulating both preemptive signalling and information integration.