Cytomegalovirus Infections

At various time points following addition of labeled DMEM, metabolites were harvested as previously described.^{20 (link)} After drying the samples, the metabolites extracted from the infected plates were dissolved in 600 µL of HPLC-grade water, while metabolites from mock-treated plates were dissolved in 300 µL. This 2-fold difference in volume accounts for the ~2-fold increase in volume of the fibroblasts during human cytomegalovirus infection. Volumes of 10 µL of each metabolite extract were analyzed via reversephase ion-pairing chromatography coupled to a stand-alone orbitrap mass spectrometer. The mass spectrometer scan rate was set to 1 Hz and resolving power to 100 000, scanning m/z 85–1000 in the negative ion mode. All other parameters are as in Lu et al.^{21 (link)} The LC gradient was 0 min, 0% B; 2.5 min, 0% B; 5 min, 20% B; 7.5 min, 20% B; 13 min, 55% B; 15.5 min, 95% B; 18.5 min, 95% B; 19 min, 0% B; 25 min, 0% B. Solvent A is 97:3 water–methanol with 10 mM tributylamine and 15 mM acetic acid; solvent B is methanol. The flow rate was 200 µL/min on a Synergy Hydro-RP column (100 mm × 2 mm, 2.5 µm particle size, Phenomenex, Torrance, CA).

Our goal was to use ratings of surprised faces to calculate each individual’s bias score. We used the facial expressions of clear valence (angry and happy) to first determine that participants could accurately rate the valence of these expressions. Recall that the 17-ms duration condition was selected as a comparison condition that participants would not be able to reliably identify (Ogawa & Suzuki, 1999 (link)). Consistent with this assertion, explicit behavioral responses for faces with a clear valence (i.e., angry, happy) in the 17-ms condition were not significantly different from chance, angry: t(29) = 1.93, p > .05, d_z = .35 (M = 43.8%, SD = 18.6%); happy: t(29) = 1.00, p > .3, d_z = .18 (M = 45.9%, SD = 18.0%). Conversely, ratings for the 50- and 1,000-ms presentation durations were accurate (i.e., different from chance) angry at 50 ms: t(29) = 21.19, p < .001, d_z = 3.87 (M = 89.1%, SD = 9.6%); angry at 1,000 ms: t(29) = 44.06, p < .001, d_z = 8.04 (M = 95.9%, SD = 5.5%); happy at 50 ms: t(29) = 20.61, p < .001, d_z = 3.76 (M = 10.5%, SD = 10.1%); happy at 1,000 ms: t(29) = 41.69, p < .001, d_z = 7.61 (M = 4.2%, SD = 5.8%). Because participants could not discriminate the clearly valenced expressions at 17 ms, we based calculation of participants’ bias scores for ratings of surprised faces on 50- and 1,000-ms presentations only. That said, once we determined each participants’ bias score we included all stimulus durations in the EMG analysis. This is consistent with our theoretical framework outlined in the Introduction suggesting that EMG responses are spontaneous and automatic in that they do not differ based on stimulus duration, even very short stimulus durations that produce differences in subjective report (i.e., 30 ms; Dimberg et al., 2000 (link)). Note that, inclusion of the 17-ms condition here is done within an omnibus analysis that will detect any main effects of duration and/or Duration × Expression interaction if this condition should turn out to systematically differ in the present study (see Results).