View source for Medicine:Riddoch syndrome

{{short description|Type of visual impairment}}
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'''The Riddoch syndrome''' is a term coined by Zeki and Ffytche (1998) in a paper published in ''Brain''.<ref name=":0" /> The term acknowledges the work of George Riddoch who was the first to describe a condition in which a form of [[Medicine:Visual impairment|visual impairment]], caused by [[Medicine:Lesion|lesion]]s in the [[Biology:Occipital lobe|occipital lobe]], leaves the sufferer blind but able to distinguish visual stimuli with specific characteristics when these appear in the patient's blind field. The most common stimuli that can be perceived ''consciously'' are the presence and direction of fast moving objects (moving at a speed in excess of 10 degrees per second); in his work these moving objects were described as "vague and shadowy". Riddoch concluded from his observations that "movement may be recognized as a special visual perception".<ref name=":1" />

Riddoch's description was dismissed by Sir Gordon Holmes in a 1918 paper<ref name=":2">{{cite journal | vauthors = Holmes G | title = Disturbances of Visual Orientation | journal = The British Journal of Ophthalmology | volume = 2 | issue = 9 | pages = 449–68 | date = September 1918 | pmid = 18167816 | pmc = 513529 | doi = 10.1136/bjo.2.9.449 }}</ref> in which he wrote that "The condition described by Riddoch should not be spoken of as a dissociation of the elements of visual sensation" because "occipital lesions do not produce true dissociations of function with intact retinal sensibility".<ref name=":2" />  The idea of a separate representation of visual motion was further dismissed by H.L. Teuber <ref>{{Cite book| vauthors = Teuber HL |title=Perception, Handbook of Physiology|publisher=Am. Physiological Society|year=1960}}</ref> and, in general, such an idea was not accepted until physiological studies in the monkey demonstrated the existence of a cortical area lying outside the primary visual cortex (area V1) in which almost all cells were selective for directional motion.<ref>{{Cite journal|date=1971-12-24|title=Response properties and receptive fields of cells in an anatomically defined region of the superior temporal sulcus in the monkey |journal=Brain Research|language=en|volume=35|issue=2|pages=528–532|doi=10.1016/0006-8993(71)90494-X |last1=Dubner |first1=R. |last2=Zeki |first2=S.M. |pmid=5002708 }}</ref><ref>{{cite journal | vauthors = Zeki SM | title = Functional organization of a visual area in the posterior bank of the superior temporal sulcus of the rhesus monkey | journal = The Journal of Physiology | volume = 236 | issue = 3 | pages = 549–73 | date = February 1974 | pmid = 4207129 | pmc = 1350849 | doi = 10.1113/jphysiol.1974.sp010452 }}</ref> With that new knowledge,  a new study of patient GY, who had  been used extensively to demonstrate the phenomenon of [[Philosophy:Blindsight|blindsight]] (that is to say the ability to discriminate correctly visual stimuli presented to the blind field without conscious awareness) led to interesting findings. The re-examination showed that, when presented with fast-moving, high contrast, visual stimuli in his blind field, he could discriminate their presence and direction of motion ''consciously'',<ref>{{cite journal | vauthors = Barbur JL, Watson JD, Frackowiak RS, Zeki S | title = Conscious visual perception without V1 | journal = Brain | volume = 116 ( Pt 6) | issue = 6 | pages = 1293–302 | date = December 1993 | pmid = 8293272 | doi = 10.1093/brain/116.6.1293 }}</ref><ref name=":0" /> This, in turn, led to a re-classification of blindsight into Type 1 and Type 2<ref>{{Cite journal| vauthors = Weiskrantz L |date=1998|title=Consciousness and Commentaries |journal=International Journal of Psychology|language=fr|volume=33|issue=3|pages=227–233|doi=10.1080/002075998400411 |citeseerx=10.1.1.611.3468}}</ref> the former adhering to the previous definition of blindsight while the latter acknowledging the fact that the experience of such subjects can be conscious even if much degraded.

Only moving objects in the [[Medicine:Scotoma|scotoma]] are visible, static ones being invisible to the patient.<ref name=":1">{{cite journal | vauthors = Riddoch G |date=1917 |title=Dissociation of visual perceptions due to occipital injuries, with especial reference to appreciation of movement |journal=Brain |publisher=[[Organization:Oxford University Press|Oxford University Press]] |volume=40 |issue=1 |pages=15–57 |doi=10.1093/brain/40.1.15 }}</ref> The moving objects are not perceived to have color or detail.  The subject may only have awareness of the movement without visual perception of it (gnosanopsia),<ref name=":0">{{cite journal | vauthors = Zeki S, Ffytche DH | title = The Riddoch syndrome: insights into the neurobiology of conscious vision | journal = Brain | volume = 121 ( Pt 1) | issue = 1 | pages = 25–45 | date = January 1998 | pmid = 9549486 | doi = 10.1093/brain/121.1.25 | publisher = [[Organization:Oxford University Press|Oxford University Press]] | doi-access = free }}</ref> or the general shape of a moving object may be perceivable as a shadow-like outline.<ref name="ATC" /> The syndrome is named after George Riddoch who had been a temporary officer in the Royal Army Medical Corps and examined soldiers who were blinded by gunshot wounds to their brains.<ref name=":0" />

At least one patient was able to use a rocking chair—putting non-moving surroundings in relative motion to her head—to improve her motion perception. She eventually was able to do the same with movement of her head.<ref name="ATC">{{Cite episode |series=All Things Considered |network=NPR |station=WAMU |date=26 May 2014 }}</ref>

== See also ==
* {{annotated link|Philosophy:Blindsight}}
* {{annotated link|Biology:Visual agnosia}}

== References ==
{{Reflist|30em}}

{{Eye pathology}}

[[Category:Ophthalmology]]
[[Category:Syndromes]]

{{Sourceattribution|Riddoch syndrome}}