Exp Brain Res (2011) 209:19–27 Fig. 3 Individual masking curves. Focused on the time windows of interest (blue SOAs 70–110), the individual performances over SOAs (between 50 and 130 shown) are presented. Note that proportion cor- rect is on the vertical axis, but that the scale varies across participants. The individual curves are expectedly noisier than the group curve, and not every participant displays the group pattern in his/her individual performance. But the individual curves demonstrate that the group eVect is not an artifact of averaging, and indeed many participants dis- play more than one dip the multiple dips in the group map are an averaging artifact based on two or three outliers. Thus, altogether, our data seem to reveal at least two performance dips within the classical-masking time window around 100 ms. Subjective visibility ratings Interestingly, the group masking curve on subjective report of visibility did not correspond well to the performance curve (Fig. 2, lower graph). The no-TMS rating was above all TMS pulse time windows, from 0 to 150 ms SOA. When taking, for instance, the visibility rating of time win- dow 0 ms as a reference, there is hardly a deviation across time windows. On a scale of 1–4, in which values 1 and 2 represent ‘I didn’t see it’ and values 3 and 4 represent ‘I did see it’ (to simplify), the average rating was around 2.5—the border between reporting ‘seen’ versus ‘unseen’. This shows that our stimuli really were diYcult to perceive, as was our intention in establishing a sensitive TMS-masking paradigm. When performing the statistical comparison of individual time windows versus all-round mean, again two time windows reveal a signiWcant TMS eVect; 120 and 140 ms (t(9) = 3.23; P < 0.05, and t(9) = 1.84; P < 0.05, respectively—see Table 1 for all t and P values). It thus seems to make a diVerence which measure of visual aware- ness is adopted, when TMS-masking eVects seem to occur in a sensitive TMS-masking paradigm. However, we should point out that, although signiWcant, the eVects here were exceedingly small. On a scale of 1–4, the diVerences between the 120 and 140 ms time windows to the average visibility rating were only 0.14 and 0.15, respectively. For comparison, we note that in a diVerent (non-sensitive) TMS-masking study using the same scale (de Graaf et al., in preparation), we found a masking eVect on subjective visibility rating around 1.5, which is a full order of magni- tude larger. Nonetheless, we acknowledge the statistically signiWcant comparisons. And eVect sizes in the objective discrimination task were small as well, compared to mask- ing eVects in non-sensitive paradigms. This is to be expected when stimulating at lower intensities than is con- ventional. This might lead one to suggest that objective vision is disturbed by TMS before subjective vision (70–90 vs. 120– 140 ms, respectively). However, we caution that this is not 25 a valid conclusion based on these results alone. An appro- priate analysis to address this question speciWcally is to look at individual peak masking latencies for objective masking, and for subjective masking, and to compare these directly in a within-subject contrast (see “Methods”). This analysis suggests that the average peak masking latencies for objective and subjective masking curves were 97.5 (SD 27.0) ms and 90.0 (SD 41.4) ms SOA respectively, and not signiWcantly diVerent (t(9) = 0.7; P = 0.50). In our view, it seems that the objective masking curve is interesting and potentially very revealing. The subjective masking curve may not have been sensitive enough to detect these fragile eVects. Discussion We here present an exploration of TMS-masking eVects at diVerent time windows from visual target stimulus onset, using a sensitive TMS-masking paradigm and two mea- sures of visual awareness. We set out to investigate whether a sensitive TMS-masking paradigm might yield diVerent masking curves from those revealed previously. Also, we were interested in whether subjective and objective mea- sures dissociate diVerentially over time. Objective versus subjective measures of visual awareness over time Methodologically, we Wnd that the subjective rating mea- sure of visibility was, in the current study, not sensitive enough to obtain convincing masking eVects in the classi- cal-masking window (60–120 ms, see “Introduction”). This is in line with our experiences using the subjective scale, which generally results in the same pattern of masking eVects as objective measures of vision, but is less sensitive chronometrically (de Graaf et al. in preparation). At any rate, in this study the behavioral masking eVects observed within the classical-masking time window were not mir- rored by the subjective measure. The fact that TMS aVected discrimination performance but not subjective visibility rat- ings in time-speciWc windows is, strictly speaking, a disso- ciation (de Graaf and Sack 2011). But it is a dissociation opposite to the TMS-induced blindsight that has been reported before (Boyer et al. 2005; Jolij and Lamme 2005). These studies reported that, in the absence of subjective vision, performance was unhampered. In our case, it would seem that with decreased performance, subjective vision was unhampered. But it seems more straightforward to con- clude that our measure of subjective vision was less sensi- tive than the measure of objective vision, than to postulate that objective vision can be disrupted while conscious experience is unchanged. In this regard, it is relevant to 123