Seeing Invisible Months: Homonymous Hemianopia in a Sequence-Space Synaesthete
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LH, a sequence-space synaesthete with a complete homonymous hemianopia (loss of vision in the left visual field of both eyes) was tested with a control group from the normal population on tasks of auditory semantic categorisation, mental imagery and date bisection. It was established that she is able to “see” the months from her spatial representation of the calendar year which appear in her blind visual field. LH was significantly faster at categorising months which appear in her blind visual field versus her preserved visual field. It is suggested that her blind field acts as a blank canvas, and she is thus faster at categorising blind months as there is no interference from visual stimuli. In the dot imagery task LH made significantly more errors when arrows indicated dots which had appeared in her right visual field, supporting the argument for her blind field functioning as a blank canvas. In the month imagery task LH was more likely to make errors when arrows indicated areas which had contained months in incongruent locations. It is suggested that this was due to interference from her sequence-space synaesthesia, as placing months in incongruent locations forced her to re-direct her attention. In the date bisection task, LH’s spatial representation of the months gave her an advantage over controls and she was significantly more likely to choose the correct midpoint. Controls appeared to be manipulating a mental calendar in the shape of an ellipse, and displayed pseudoneglect in the form of a consistent spatial bias to the left. In summary, LH’s homonymous hemianopia has not affected her ability to “see” her spatial representation of the months, and her blind field acted as a blank canvas. On tasks involving the months of the year her synaesthesia gave her an advantage, while placing her months in incongruent locations caused interference in the task.