When a few elements of a situation (an overall picture) change, people on the spectrum may perceive the situation as completely different. I.e. when the daytime room isn’t recognized in het evening. In order to illuminate this phenomenon, we have to go back to how people construct overall pictures in the first place.
When a ‘neurotypical’ is confronted with a new object, (s)he will observe it and start with comparing it with similar objects. If it doesn’t match any of those, the person will inspect it in detail and these details will become part of a visual ‘map’, a prototype, with which the next similar object will be explored. Subsequently not all details will be inspected, but only a limited, deliberate number of them. The more experience one builds up with a particular object, the more efficient and quickly its identification will become.
Normal brains then tend to jump back and forth, between a limited number of strategic details in reality and the prototype in memory.
People with Weak Central coherence do this differently. They assemble overall pictures again and again from scratch. The resulting overall pictures do not become prototypes but remain assemblies of details, which may, as such, be stored firmly in memory. Since they aren’t transformed into more abstract, ‘higher order’ models, the person who holds them cannot play with them. He cannot alter certain properties and ‘see’ what the results are. So when confronted with a similar situation, it becomes very hard to see when only a limited number of elements have changed, while basically (in a, to the autistic mind, inexplicable way) having remained the same. Hence, people with Weak Central coherence experience a new situation which is in fact a variant of one they already know.
In her book Autism. An Inside-Out Approach Donna Williams introduces ‘Jenny’s’ as an example of ‘perceptual problems’. The severity of Jenny’s autism may account for Williams’ somewhat different description of the same phenomenon:
“Jenny refuses to look at people although she can see an entire person, she can only visually process the meaning of one bit of them at the time and only forms a mental impression from the bits of what she has seen rather than forming coherent mental images. Seeing in bits also means that Jenny defines people and places and things by these bits and she can suddenly find once familiar things to be strikingly unfamiliar if slight components have changed, such as when someone moves the furniture or doesn’t wear the same coat as usual.”