I would suggest that a critical point in the development of true consciousness came when we moved out of the forest. In the forest, the primary sensory mode was scent, the recognition and filing away of discrete molecules that conveyed specific digital meanings as to their source. Moving to the open grassland meant that proto-humans had to shift dominance from scent to sight, rather quickly on the fly. Sight is a completely different kind of processing from scent, requiring the building of internal models to compare with incoming data for estimates of parallax, for example. Both predators and prey in the grasslands had already evolved that were primarily sight-based, as it was necessary to spot food or danger over fairly large distances over which scent alone was too dependent upon the prevailing wind to be reliable enough.
The separate and distinct modalities required a mechanism to integrate the disparate data and make a good choice as to action. I.e., instead of a one-to-one correspondence between sensation or perception of scent vs. sight, the processing and feedback loops became tangled and begged the question of how to weight incomensurate variables. Thus, there had now to also be another layer of processing that was concerned with mental events as such. Such, I contend, might have been the critical take off point to real consciousness.
One kind of mental event is "music." Music, like visual art, can be experienced with no concrete representational component. Consider opera or music with lyrics in general vs. music with lyrics but in a language not understood, so that the voice is effectively just another instrument, albiet with some concrete emotional content. The forms of music match up with those available as part of the processing patterns inherent in brain function, which is why music is often maddeningly impossible to screen out. But that suggests that a study of music might be correlated with actual synched brain activity, as has long been suggested by advocates of various "hemi-sync" vendors and researchers.