Observers of schizophrenia have wanted to summarise the basic fault upon which the subsequent symptoms and behaviour could be understood.
One such attribute was a failure to sort out what needed to be attended to, to engage with the outside world.

The most consistent position is that persistent emotional unsettling, particularly hostile amd directed, disturbs, and makes the illness, acute and florid.

The anatomy for this is a hypereractivity in the ventral hippocampus following a startle upping of firing from the hippocampus after midbrain tegmentum 'gain'

That leaves to be decided what is the persistent change that continues the illness in its quieter phases.

Decreased activity in the parahippocampal gyrus of the POCs was observed during all three conditions of attention.
The parahippocampal gyrus surrounds the hippocampus and lies in the medial temporal lobes of the brain.
It has been argued that a disordered 'hippocampal formation' (i.e., hippocampus and parahippocampal gyrus) is the fundamental abnormality in the pathophysiology of schizophrenia based on decreased size, reduced N-acetyl aspartate, altered metabolic/synaptic activity, presence of memory deficits (attributable to hippocampal dysfunction), and alterations in receptors [39-42].
In addition to the role of the hippocampus in memory formation, it has also been suggested that it plays a crucial role in integrating multimodal sensory inputs,
and in resolving conflicts between expectancies and the current perception [43,44]. This is in accord with the role of the hippocampus in encoding attention proposed by Mirsky et al. [1

updated

Others consider thought disorder of some kind to be the basic fault

a beginning a 1998 viewpoint

Attention

clinical observations

One of the striking features of the sufferer from schizophrenia in the old mental hospitals was the seeming indifference to widespread dental diseae which ordinarily could be expected to cause pain and drive attention for a remedy. Similarly a paient with a heart arrythmia described only bird wings in his chest-; another ignored as pecking ,what would have been the anginal pain of a heart condition .

a review of attention studies

Once doing a ward round - the first two days, new patients were in or around their beds, getting used to medication, and the nurses, as nurses - I introduced myself 'Dr Y I will be looking after you here - what's your name ,,,, to be answered by a patient three beds down suffering from schizophrenia who answered as though it was a Q. addressed to her . It was 'forced' out of her; she could not set it aside, giving her time.