Also important has been a line of argumentation by philosophers that the subjective nature of consciousness makes it inherently difficult to study. Block's (1995) influential distinction between phenomenal and access consciousness was framed as part of a critique of treatments of consciousness in the psychological literature: by failing to properly distinguish between consciousness as experience (phenomenal consciousness) and consciousness as general availability of information (access consciousness), scientists were equivocating — drawing conclusions about consciousness in the phenomenal sense from premises about consciousness in the access sense. The conceptual distinction between access consciousness and phenomenal consciousness, and the difficulty of gaining empirical traction on the latter, has been seen as a major hurdle to empirical consciousness studies. Block himself has recently been more optimistic, even arguing that certain experiments can empirically tease apart phenomenal and access consciousness (Block 2011). But the distinction between access and phenomenal consciousness does raise special methodological hurdles for those who want to study the latter empirically.