Spatial visual attention

In this thesis, we will focus on how attention works on spatial visual attention, e.g. on how cueing one location at a time can influence the detection of a visual following stimulus. One of researchers goals is the transformation of complex phenomena into simpler mental operations that can be related to neural systems. Thus, Posner (1980) decided to investigate detection of simple sensory events with the idea that luminance increments in dark fields would facilitate the understanding of how spatial visual attention works. His study of attention divided it in three components: alertness, selectivity and processing capacity. In tasks that researchers design to study attention, the ability to develop and maintain an optimal sensitivity to environmental stimulation is investigated when participants receive a signal to prepare themselves at different intervals. The first component, alertness, must be developed rapidly and maintained over a relatively short period during this time waiting before a reaction time task. The second component of attention is the ability to select information from one source or one kind rather than another. This component was classically investigated in giving clues to the participants about what he has to look for. The third component, the processing capacity, is related to the idea of a limited central processing capacity. It is observed that when participants have to handle many tasks at the same time; they perform worst even if they do their best.

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2.3.1.1 The cueing Posner task

Posner et al. (1978), wanted to know if shifts in covert attention exist. Tasks based on participants response time have been created to investigate the covert orienting by measuring the efficiency of detecting events that appear at different spatial locations (Posner, Nissen, &

Ogden, 1978). If the efficiency of detecting an event was changed by orienting attention, it would prove that the line of attention would be separated from the gaze. Thus, Posner and al.

(1980) imagined a setup in which participants would respond in pressing a button as fast as possible after the presentation of a detection stimulus (a target stimulus) while the gaze is monitored with electrooculography. In this way, they could test if participants detect more rapidly the target when they knew where the stimulus would appear, even if no movements of eyes were observed. Three conditions were designed: 1) neutral, 2) valid trials, and 3) invalid trials (Figure 3). A neutral trial was a non-informative plus sign as a cue followed by a detection stimulus to the left or the right. A valid trial had an arrow as a cue, showing the side where the target stimulus is going to appear. An invalid trial was made of an arrow as a cue, showing the opposite side of the location of the target. This design gave the opportunity to calculate the cueing effect and distinguish both the benefits and the cost of it.

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Figure 3: Original task of Posner: valid (cued) and invalid (uncued) trials. The SOA (Stimuli Onset Asynchrony) is the time between the cue onset to the target onset. From Klein, 2000.

The cueing effect or the facilitation effect is the difference between average reaction time of valid and invalid trial. It reflects the strength of the spatial orientation by the cue and it is constituted by benefits and costs. Benefits are calculated by the difference between the reaction time for neutral trial and the reaction time when the attention is cued to the place in space where the stimulus occurs (i.e a valid trial). Benefits reflect at what point the participant’s spatial attention was efficiently cued. However, the difference of reaction time between neutral trial and invalid trial determined the cost, thereby; it represents how long it took to re-orientate your attention from the uncorrected cue to the target. Different variants of the task were explored (letter vs digit or higher vs lower than the cue) and they discovered that the more the task is difficult, the less is the overall effect (Posner, 1980).

Classically, this unimodal Posner task with visual stimuli as cues and targets has been used (Shulman, Remington, & Mclean, 1979) but an increasing number of studies started to

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investigate the capabilities to orient and report attention with different modalities and across-modalities.

At first, experimental research focused on simple cueing such as luminance increments. Later, in the 1990’s, they tested the negative emotion of fear with the use of fearful faces or anger faces as cues (Mogg & Bradley, 1998; Vuilleumier, Armony, Driver, & Dolan, 2001). More broad threatening stimuli were then investigated on individuals with and without anxiety (Bar-Haim, Lamy, Pergamin, Bakermans-Kranenburg, & Van Ijzendoorn, 2007). Recently, studies expanded the investigation of attentional biases to rewarding stimuli (Brosch, Sander, Pourtois,

& Scherer, 2008; Pool, Brosch, Delplanque, & Sander, 2016). Their studies have shown that the spatial cueing effect is affected by various stimuli.

2.3.1.2 Common pool of attentional resources between modalities

Since the seventies, the idea of a limited capacity of attention has been brought to the front of the scene. Human senses are usually exposed to multiple stimuli at the same time that cannot be processed at the same time (Desimone & Duncan, 1995). Dividing attention between two objects almost always results in poorer performance than focusing attention on one (Kastner, De Weerd, Desimone, & Ungerleider, 1998). Moreover, attentional capacity is weakened when two different modalities are targeted (Duncan, Martens, & Ward, 1997). Nevertheless, the attentional orientation can be cued by a stimulus that will influence the integration of a following stimulus. For example, spatial informative clues, given by audio and tactile cues influence the reaction time of audio and tactile targets (Lloyd, Merat, McGlone, & Spence, 2003), audio cues can influence participant’s reaction time to olfactory or audition targets (Spence, Kettenmann, Kobal, & McGlone, 2001; Spence, McGlone, Kettenmann, & Kobal, 2001), and visual cues can influence participant’s reaction time to olfactory or tactile targets (Spence, Kettenmann, Kobal, & McGlone, 2000).

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Thus, spatial attention can be oriented by stimuli in one modality that the integration of following stimuli in another modality. Other aspects of the spatial cueing task such as the cue modality and the SOA will be discussed in the next section.

2.3.1.3 Modality and timing

Additionally, the cueing modality and the timing are critical aspects that go together (Spence, 2010). The most critical time is the delay between the start of the cue and the start of the target, which is named stimulus onset asynchrony (SOA). This SOA is typically varied during the experiment to avoid automatic answers from participants. Plotting reaction time versus SOA (Figure 4), it can be seen that for some values of SOA, the cueing effect disappear or is reversed.

This reversed effect is called the inhibition of return (Klein, 2000). For visual cues, the attention orientation occurs with a SOA from 0 to ~100 ms, disappear with a SOA from ~100 to ~300 ms and the inhibition of return effect appears with a SOA from ~300 to ~500 and ~2400 ms (Palanica & Itier, 2015).

Figure 4: Typical results of Posner task of reaction time on SOA (ms). From Klein, 2000. Black dots are valid trial averages and white dots are invalid trial averages.

For audio cues, the inhibition of return effect appears later with a SOA of around 1150 ms (Lloyd & McGloneF, 2000). Indeed, audio and visual stimuli have different speeds of

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integration (Millot et al., 2002) and chemosensory related processes of integration are known to be slow (Bensafi, Rouby, Farget, Vigouroux, & Holley, 2002; Boesveldt, Frasnelli, Gordon,

& Lundström, 2010; Croy, Krone, Walker, & Hummel, 2015; Demattè, Sanabria, & Spence, 2009). In the next section, only exogenous cueing tasks with peripheral chemosensory cues will be examined.

2.3.1.4 Chemosensory cueing in Posner tasks

Since exogenous cueing reflects an automatic natural way of orientation and can be interpreted as an adaptive tool from an evolutionary point of view, we will focus on studies with modified Posner tasks that are cued exogenously with chemosensory stimulations. In one study, the Posner task was adapted with chemosensory stimulations as cues and audio stimulations as targets (La Buissonnière-Ariza, Frasnelli, Collignon, & Lepore, 2012). La Buissonnière-Ariza et al. (2012) used phenyl ethyl alcohol (odor similar to rose, which is an almost pure olfactory stimulant) as the olfactory stimulus, eucalyptol as the chemosensory stimulus, air puffs for the somatosensory stimulus and nothing at all for the control stimulus (2L/min in each nostril).

Participants were asked to hold their breath from just before the cue until to after their response.

The cues were delivered 600 ms before the lateralized audio target. Participants had to respond as fast and as accurately as possible by pressing one of two buttons in order to indicate the side of the audio target. All cueing conditions enhanced the responding abilities of participants, but no effect depending on the validity of trials (cueing effect) was observed.

Then, another adapted Posner task was used with phenyl ethyl alcoho diluted at 3/40 for 1500 ms, as the cue, delivered in a heated humidified airflow at ~7L/min with visual stimulation as targets (Moessnang, Finkelmeyer, Vossen, Schneider, & Habel, 2011). Participants were asked to breathe through their mouth. The control condition was made of distilled water. The visual targets appeared after 500 ms of the olfactory cue, and for 1000 ms (Figure 5). Participants had to answer as fast and as accurately as possible, indicating on which side the target, a

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parallelogram, appeared. Moessnang et al. (2011) found that the participants had a better accuracy in the trials with odor cues than without odor cues in the beginning of their experiment, even if they were not able to indicate the side of the phenyl ethyl alcohol stimulation (mean accuracy = 48.4%). Concerning the reaction time, they showed that men responded faster than women and that participants responded faster to right-sided targets than left-sided targets. They also found that participants were slower for valid trials than for invalid trials at the beginning of the experiment.

Figure 5: Task from Moesnnang et al., 2011.

Wudarczyk et al., 2016 used almost the same protocol of Moesnnang et al., 2011, but with a phenyl ethyl alcohol at ratio of 3/20, a trigeminal cueing constituted by CO2 cues and with an chemosensory stimulation that stop before the visual target. They found no general effect with phenyl ethyl alcohol cues, and replicated the results found in Moesnnang et al., 2011. For the CO2 cues, they used a simplified staircase procedure to determine individually the concentration embedded in the continuous airflow as well as discernible but not painful stimulation. They found no effect on the reaction times, but a significant enhancement of accuracy for valid trials only in the second half of the experiment.

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Trigeminal stimulations may influence spatial attention but these studies failed to discover a clear effect. In the next section, we will see the technical challenges necessary for doing chemosensory cueing.

2.3.1.5 The technical challenges of delivering chemosensory stimulations as cues

Only a state-of-the-art olfactometer can deliver reliably, in a reproducible manner, stimulants at definite time in the range of ms, without odor contaminations or stimulating the trigeminal system in any other way than chemically (Ischer et al., 2014). The first key aspect of the Posner task is a precise cueing timing, so the delivering of volatile stimulant has to be very accurate.

If the SOA is too short or too long, the cueing effect may not occur. Moreover, the cueing is supposed to stop before the target appears. The second crucial key aspect is the concentration reliability. The spatial attention has to be cued with the same concentration from the beginning to the end of the experiment. The third key aspect is avoidance of cross-contamination. This latter is the contamination of one odorant by remaining traces of the preceding one. If one odor contaminates the olfactometer, the control trials will be impaired. The fourth key aspect, for the same reason, is the pollution of the ambient air. The fifth key aspect is avoiding of triggering any trigeminal stimulation other than the chemical one. Technically, there are two strategies.

The first one is to humidify and heat the air sent to the participants. The second one is to choose a flow rate (around 1L/min) that does not elicit pain anymore (Lorig, Elmes, Zald, & Pardo, 1999) and to have minimal change of flow between cueing puffs and constant flow. To test if the chemosensory stimulation is appropriate for cueing, a lateralization test (as seen in the investigation of the trigeminal system part) can be run. If participants can report in which nostril the stimulation has been delivered, the probability to create a cueing effect might be higher.

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