Limits...
Seeing without Seeing? Degraded Conscious Vision in a Blindsight Patient.

Overgaard M, Fehl K, Mouridsen K, Bergholt B, Cleeremans A - PLoS ONE (2008)

Bottom Line: In our single case study of patient GR, we ask whether blindsight is best described as unconscious vision, or rather as conscious, yet severely degraded vision.In experiment 1 and 2, we successfully replicate the typical findings of previous studies on blindsight.The third experiment, however, suggests that GR's ability to discriminate amongst visual stimuli does not reflect unconscious vision, but rather degraded, yet conscious vision.

View Article: PubMed Central - PubMed

Affiliation: CNRU, Hammel Neurorehabilitation and Research Center, Aarhus University Hospital, Hammel, Denmark. neumov@sc.aaa.dk

ABSTRACT
Blindsight patients, whose primary visual cortex is lesioned, exhibit preserved ability to discriminate visual stimuli presented in their "blind" field, yet report no visual awareness hereof. Blindsight is generally studied in experimental investigations of single patients, as very few patients have been given this "diagnosis". In our single case study of patient GR, we ask whether blindsight is best described as unconscious vision, or rather as conscious, yet severely degraded vision. In experiment 1 and 2, we successfully replicate the typical findings of previous studies on blindsight. The third experiment, however, suggests that GR's ability to discriminate amongst visual stimuli does not reflect unconscious vision, but rather degraded, yet conscious vision. As our finding results from using a method for obtaining subjective reports that has not previously used in blindsight studies (but validated in studies of healthy subjects and other patients with brain injury), our results call for a reconsideration of blindsight, and, arguably also of many previous studies of unconscious perception in healthy subjects.

Show MeSH

Related in: MedlinePlus

Probability of correctly identifying the stimulus given a “seen” vs. “unseen” report (Dichotomous Report) or given a “Clear Experience/Almost Clear Experience” vs. a “Weak Glimpse/Not seen” report (PAS report), plotted separately for the Intact and Blind fields".
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2507770&req=5

pone-0003028-g003: Probability of correctly identifying the stimulus given a “seen” vs. “unseen” report (Dichotomous Report) or given a “Clear Experience/Almost Clear Experience” vs. a “Weak Glimpse/Not seen” report (PAS report), plotted separately for the Intact and Blind fields".

Mentions: To further illustrate the relationship between PAS and binary report, we split the PAS data in different ways. We note that the pattern of correct and incorrect reports obtained by pitting PAS “clear image” reports against the other three categories is almost identical to that obtained when GR was asked to gave binary reports. This suggests that GR is setting her threshold for reporting awareness too high under binary report conditions. If, instead, the cut-off for awareness is placed between scale points “almost clear image” and “weak glimpse” (Table 1c) we would conclude that GR has a high degree of awareness of stimuli presented in the injured part of her visual field, since there is a correlation between awareness and accuracy (p = 0.0004, Fisher's exact test). An illustration of turning the PAS reports into a binary measure is also shown in figure 3.


Seeing without Seeing? Degraded Conscious Vision in a Blindsight Patient.

Overgaard M, Fehl K, Mouridsen K, Bergholt B, Cleeremans A - PLoS ONE (2008)

Probability of correctly identifying the stimulus given a “seen” vs. “unseen” report (Dichotomous Report) or given a “Clear Experience/Almost Clear Experience” vs. a “Weak Glimpse/Not seen” report (PAS report), plotted separately for the Intact and Blind fields".
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2507770&req=5

pone-0003028-g003: Probability of correctly identifying the stimulus given a “seen” vs. “unseen” report (Dichotomous Report) or given a “Clear Experience/Almost Clear Experience” vs. a “Weak Glimpse/Not seen” report (PAS report), plotted separately for the Intact and Blind fields".
Mentions: To further illustrate the relationship between PAS and binary report, we split the PAS data in different ways. We note that the pattern of correct and incorrect reports obtained by pitting PAS “clear image” reports against the other three categories is almost identical to that obtained when GR was asked to gave binary reports. This suggests that GR is setting her threshold for reporting awareness too high under binary report conditions. If, instead, the cut-off for awareness is placed between scale points “almost clear image” and “weak glimpse” (Table 1c) we would conclude that GR has a high degree of awareness of stimuli presented in the injured part of her visual field, since there is a correlation between awareness and accuracy (p = 0.0004, Fisher's exact test). An illustration of turning the PAS reports into a binary measure is also shown in figure 3.

Bottom Line: In our single case study of patient GR, we ask whether blindsight is best described as unconscious vision, or rather as conscious, yet severely degraded vision.In experiment 1 and 2, we successfully replicate the typical findings of previous studies on blindsight.The third experiment, however, suggests that GR's ability to discriminate amongst visual stimuli does not reflect unconscious vision, but rather degraded, yet conscious vision.

View Article: PubMed Central - PubMed

Affiliation: CNRU, Hammel Neurorehabilitation and Research Center, Aarhus University Hospital, Hammel, Denmark. neumov@sc.aaa.dk

ABSTRACT
Blindsight patients, whose primary visual cortex is lesioned, exhibit preserved ability to discriminate visual stimuli presented in their "blind" field, yet report no visual awareness hereof. Blindsight is generally studied in experimental investigations of single patients, as very few patients have been given this "diagnosis". In our single case study of patient GR, we ask whether blindsight is best described as unconscious vision, or rather as conscious, yet severely degraded vision. In experiment 1 and 2, we successfully replicate the typical findings of previous studies on blindsight. The third experiment, however, suggests that GR's ability to discriminate amongst visual stimuli does not reflect unconscious vision, but rather degraded, yet conscious vision. As our finding results from using a method for obtaining subjective reports that has not previously used in blindsight studies (but validated in studies of healthy subjects and other patients with brain injury), our results call for a reconsideration of blindsight, and, arguably also of many previous studies of unconscious perception in healthy subjects.

Show MeSH
Related in: MedlinePlus