Increased sensitivity after repeated stimulation of residual spatial channels in blindsight

Sahraie, Arash; Trevethan, Ceri T.; MacLeod, Mary Joan; Murray, Alison; Olson, John A.; Weiskrantz, Lawrence

doi:10.1073/pnas.0607073103

Cited by 157 publications

(146 citation statements)

References 27 publications

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“…We have recently shown that subjects can be trained to perform on and to see stimuli that are initially invisible to them (9). We thus hypothesize that awareness is trainable, a conclusion that is in accordance with recent findings in blindsight patients (10). However, the time course of those learning effects has not been explored, i.e., whether the improvements in sensitivity and subjective awareness depend on each other.…”

supporting

confidence: 70%

Subjective and objective learning effects dissociate in space and in time

Schwiedrzik

Singer

Melloni

2011

Proc. Natl. Acad. Sci. U.S.A.

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Perceptual learning not only improves sensitivity, but it also changes our subjective experience. However, the question of how these two learning effects relate is largely unexplored. Here we investigate how subjects learn to see initially indiscriminable metacontrast-masked shapes. We find that sensitivity and subjective awareness increase with training. However, sensitivity and subjective awareness dissociate in space: Learning effects on performance are lost when the task is performed at an untrained location in another quadrant, whereas learning effects on subjective awareness are maintained. This finding indicates that improvements in shape sensitivity involve visual areas up to V4, whereas changes in subjective awareness involve other brain regions. Furthermore, subjective awareness dissociates from sensitivity in time: In an early phase of perceptual learning, subjects perform above chance on trials that they rate as subjectively invisible. Later, this phenomenon disappears. Subjective awareness is thus neither necessary nor sufficient for achieving above-chance objective performance.consciousness | psychophysics | Signal Detection Theory O ur perceptual apparatus is constantly shaped by experience. This fact has been shown, for example, in experiments investigating perceptual learning, where practice on a sensory task leads to increases in perceptual sensitivity (1). Although perceptual learning is a well-studied phenomenon, the question of how it changes subjective awareness has rarely been addressed. Do we actually "see more" after training? Apart from anecdotal reports pointing in this direction, a quantitative analysis of the effects of learning on subjective awareness is largely missing (2) because studies in perceptual learning have almost exclusively focused on objective task performance [i.e., sensitivity in terms of signal detection theory (3)]. However, studies from a different line of research, namely those investigating conscious perception, have found that objective performance in a task and awareness of the stimuli on which the task is performed can dissociate. Such is the case in blindsight (4) but also is found in normal observers (refs. 5-7 but see ref. 8). These data demonstrate that these two aspects of perception cannot be treated as being equivalent. We have recently shown that subjects can be trained to perform on and to see stimuli that are initially invisible to them (9). We thus hypothesize that awareness is trainable, a conclusion that is in accordance with recent findings in blindsight patients (10). However, the time course of those learning effects has not been explored, i.e., whether the improvements in sensitivity and subjective awareness depend on each other. In particular, changes in sensitivity could be a prerequisite for changes in subjective awareness. Alternatively, it could be necessary to subjectively see a stimulus in order for changes in sensitivity to occur. Last but not least, training could affect sensitivity and subjective awareness in parallel without any mut...

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supporting

confidence: 70%

Subjective and objective learning effects dissociate in space and in time

Schwiedrzik

Singer

Melloni

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…Previous research on a number of cases with blindness after brain injury shows that repeated exposure to first-order stimuli over a period, using an experimental paradigm similar to those reported here, can lift performance from chance to well-above-chance levels, but without awareness (type I blindsight). Further systematic exposure to first-order stimuli over extended periods of time can result in type II performance (19,20). It would be of interest to investigate whether transition from type I to type II would be less likely with repeated stimulation with second-order stimuli.…”

Section: Discussionmentioning

confidence: 99%

Consciousness of the first order in blindsight

Sahraie

Hibbard

Trevethan³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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At suprathreshold levels, detection and awareness of visual stimuli are typically synonymous in nonclinical populations. But following postgeniculate lesions, some patients may perform above chance in forced-choice detection paradigms, while reporting not to see the visual events presented within their blind field. This phenomenon, termed "blindsight," is intriguing because it demonstrates a dissociation between detection and perception. It is possible, however, for a blindsight patient to have some "feeling" of the occurrence of an event without seeing per se. This is termed blindsight type II to distinguish it from the type I, defined as discrimination capability in the total absence of any acknowledged awareness. Here we report on a well-studied patient, D.B., whose blindsight capabilities have been previously documented. We have found that D.B. is capable of detecting visual patterns defined by changes in luminance (first-order gratings) and those defined by contrast modulation of textured patterns (textured gratings; second-order stimuli) while being aware of the former but reporting no awareness of the latter. We have systematically investigated the parameters that could lead to visual awareness of the patterns and show that mechanisms underlying the subjective reports of visual awareness rely primarily on low spatial frequency, first-order spatial components of the image.S ince the early reports in the 1970s of brain-damaged human subjects who are able to discriminate visual events in the absence of self-reported conscious awareness (1, 2), an obvious but difficult question has arisen as to what stimulus properties would drive visual awareness. In nonclinical populations, a number of paradigms have been developed to examine the prerequisites. For example, in attentional-blink paradigms (3), rapid serial visual presentation demonstrates that letters or words presented within a short temporal window following a task-relevant target may be degraded. As is well known, manipulating the functional significance of targets by using the participant's name (4) or emotional stimuli (5) modulates reported perception and discrimination of stimuli. More recently, the flash suppression technique in binocular rivalry, where one eye is presented with a rapid random sequence of abstract shapes while a specific stimulus is presented to the other eye (6), has been used to demonstrate that some classes of stimuli can break through and elicit awareness (7,8). Common among tasks presented to nonclinical subjects is the assumption that awareness of the stimuli and their discrimination, if not identical, cannot be dissociated from each other.The blindsight phenomenon in human subjects is unique: following visual cortical lesions, the detection and discrimination of stimulus features can occur in the absence of subjective awareness. For this reason, the research relies on "heroic" approaches such as forced-choice guessing (9). The reported awareness is then recorded using a commentary key paradigm on either a binary (10) or a mult...

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“…However, there is now a growing body of evidence demonstrating that perceptual training can also increase the reported perceptual awareness of stimuli in blindsight patients (e.g. Sahraie et al, 2006). Also, studies in intact subjects exposed to subliminal presentation of visual stimuli (mostly utilizing the above-mentioned metacontrast masking in a "stimulus onset asynchrony" paradigm) have demonstrated that even in individuals without injury to the brain, training can increase the degree of perceptual awareness of a stimulus originally unavailable to consciousness (e.g.…”

Section: Implications Of the Ref-model For Posttraumatic Rehabilitatimentioning

confidence: 99%

Cognitive Recovery and Rehabilitation After Brain Injury: Mechanisms, Challenges and Support

Mogensen¹

2012

Brain Injury - Functional Aspects, Rehabilitation and Prevention

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Increased sensitivity after repeated stimulation of residual spatial channels in blindsight

Cited by 157 publications

References 27 publications

Subjective and objective learning effects dissociate in space and in time

Subjective and objective learning effects dissociate in space and in time

Consciousness of the first order in blindsight

Cognitive Recovery and Rehabilitation After Brain Injury: Mechanisms, Challenges and Support

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