Upadesa Sahasri 1:34:
If pain or its causes viz., burns or cuts were in the perceiver one would have pointed out the perceiver to be the seat of the pain, like the parts of the body the seats of the burns or cuts.
1:35: Moreover, (if it were in the Self) the pain could not be perceived by the Self like the colour of the eye by the same eye. Therefore as it is perceived to have the same seat as burns, cuts and the like, pain must be an object of perception like them. Since it is an effect, it must have a receptacle like that in which rice is cooked. The impressions of pain must have the same seat as pain itself. As they are perceived during the time when memory is possible (i.e. in waking and dream and not in deep sleep), these impressions must have the same location as pain.
This are interesting parallels between these basic intuitions and familiar views in the Western tradition. We translate the idea of awareness of an external reality to the internal sensation of pain etc. Objects of perception and objects of sensation are assimilated to one another. Please note that this position is subject to the adhiropa/apavada strategy. In other words it is an interim position which is later modified on further reflection. It is subject to recension and represents the typical level of apprehension of the of the beginner. The flavour that we associate with Cartesian Dualism is there.
Next is the idea of cause and effect being in the same sphere as they interact with each other. The one is continuous with the other. In a way there is an element of weak causal closure here with the important difference that mind is regarded as inert or reflective of consciousness rather than conscious by nature. This in intimated in the following insight about the objects of consciousness. They are only present when the mind is operative viz. in waking and dream. Impressions of pain and pain itself are, like memory, in the mind. ‘In the mind’ here has not the same connotation as ‘all in your mind’ or unreal. Mind is the aspect of the physical being pervaded by consciousness.
Shankara in his succinct way has drawn the boundaries of the average intelligent seeker’s initial position. The difficulties within it are made clear by self-inquiry/atma vichara.