Qué es un microservicio y que es una aplicación monolítica

Several studies have explored the nature of pre-stimulus brain activity in an attempt to understand if this could bias observers’ subsequent perception of an

ambiguous figure using brain imaging techniques. Some studies have also investigated whether activity in the pre-stimulus period is predictive of the upcoming percept.

1.3.1.1. Functional Magnetic Resonance Imaging (fMRI) findings.

In one such study, conducted by Hesselmann, Kell, Eger and Kleinschmidt (2008), using fMRI to study the relationship between pre-stimulus brain activity and visual perception in Rubin’s face-vase illusion, results showed a high pre-stimulus activation of the right Fusiform Face Area (rFFA) when the subjects subsequently reported perceiving faces compared with the activation of that area when they reported perceiving vase percepts. Moreover, an analysis of the baseline activity before and after presentation of the stimulus (pre-stimulus vs. post-stimulus) showed a non-linear

interaction. The results from Hesselmann et al. (2008)’s study suggest two separable but complementary contributions to perceptual decisions, one related to ongoing activity, the other to stimulus-driven processes. Moreover, the results of this study suggest the initial state of the stimulus is subject to fluctuations that are slow enough to be detected by hemodynamic signals. Their results however do not show any activity in the higher frequency bands, which could be due to the low temporal sensitivity of BOLD signals. The full results of this study are described and discussed previously in this chapter (Chapter 1) in section 1.2.3.

1.3.1.2. Electroencephalography (EEG) findings.

In line with these findings, the results from Britz et al. (2009) were also suggested to be indicative of ongoing spontaneous fluctuations in the pre-stimulus period that influence subsequent percept. Britz, Landis and Michel (2009) used high resolution (256 – channel) EEG to see if pre-stimulus spontaneous fluctuations were

predictive of an upcoming perceptual reversal using the Necker Cube and found a period of activity 50 ms before stimulus onset. Their results suggest that prestimulus activity in the right inferior parietal cortex is solely linked to perceptual reversals seeing as no activity in this area was observed preceding stable trials. Pre-motor and post-stimulus activity in this area has been previously identified in fMRI studies on bistable perception (Kleinschmidt et al., 1998; Inui et al., 2000; Slotnick & Yantis, 2005) and has been linked to the appraisal of a perceptual reversal. However, due to the low temporal resolution of BOLD signals, temporal conclusions remain a challenge.

Britz et al. (2009)’s pre-stimulus findings, the momentary activity in this region seems to predict a perceptual switch of an unchanging ambiguous stimulus. Moreover, they found that this area is differentially activated only preceding reversal trials and not after stimulus onset. In EEG studies, this area of the brain has been previously linked to change detection and change blindness (Beck et al. 2001; Pessoa and Ungerleider 2004; Kim and Blake 2005; Beck et al. 2006). Ehm et al. (2011) found similar results in their study using EEG and the Necker Lattice. Their results showed an increase in lower gamma-band activity (26–40 Hz) at the right-hemispheric central and parietal electrodes and an occipital decrease of higher gamma-band activity (40–65 Hz) only on reversal trials, 200 ms before ambiguous stimulus onset. These modulations were absent in exogenous reversals of unambiguous lattice variants (Ehm et al., 2011). Britz et al. (2009) and Ehm et al. (2011) used similar experimental designs, whereby the stimulus was presented intermittently with similar presentation times and inter-trial intervals across the experiments. The main thing that differed between the two is the stimulus used. These pre-stimulus results are in line with a previous EEG study by Müller et al.

(2005) in which they used an alternating dot pattern that induced illusory motion with ambiguous direction. They found activity that dissociates between reversal and stable trials appearing in the 300 ms preceding the onset of the multistable stimulus.

In a recent study, Rassi, Wutz, Muller-Voggel and Weisz (2019) used MEG to investigate the link between pre-stimulus spontaneous fluctuations and the perceptual outcome when viewing Rubin’s Face-Vase. They used the same experimental paradigm as Hesselmann et al. (2008). Their results showed no differences in oscillatory power between face vs. vase reports in V1 or in FFA, indicating similar levels of neural excitability. This goes against previous fMRI findings (e.g. Hesselmann et al., 2008) albeit MEG may not have the spatial resolution to effectively isolate activity from these regions. However, they did find stronger connectivity of low frequency oscillations between V1 and FFA on face trials than on trials, which were reported as vases. They found that the strength of the prestimulus feedback connectivity from FFA to V1 predicted both the upcoming percept (face or vase) and the strength of post-stimulus neural activity associated with the reported percept. They found that before the onset of their Face-Vase stimulus, the FFA was more strongly connected to V1 on face reported trials, specifically in the feedback direction of FFA to V1. Connectivity between these two regions was found to take place in the alpha and beta frequency bands. They found that the time-frequency window during which the FFA was found to be mostly

predictive of the perceptual outcome was correlated with the strength pre-stimulus feedback connectivity. These findings suggest that fluctuations in neural activity before the onset of the stimulus can bias subsequent perceptual outcome. In a study by Piantoni et al. (2017) the results showed that occipital alpha oscillations during inter-trial

intervals (and therefore in the pre-stimulus period) are predictive of the duration of the sustained perceptual interpretation (stability) of the ambiguous stimulus. More

specifically, they found that high alpha power in the high-level visual cortex promotes perceptual stability.