Consciousness of the first order in blindsight

Abstract

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...

Cellular Registration without Behavioral Recall of Olfactory Sensory Input under General Anesthesia

“…The latter refers to well-documented observations that blind subjects with severely damaged primary visual cortex can still perceive unseen stimuli involving higher cortical functions. 41 …”

Inefficient search strategies in simulated hemianopia.

“…The low spatial frequency cut-off was 2 cycles per degree (for the exact method of filtering and normalizing images refer to Bannerman et al, 2012). We decided to include the 2 c/° cut-off because the remaining information was in the range of the optimal frequencies for detection and awareness in blindsight reported by Sahraie et al (2010Sahraie et al ( , 2013) and comparable to the parameters applied in previous studies by Vuilleumier, Armony, Driver and Dolan (2003) and Bannerman et al (2012). Previous work also indicated that participants were able to correctly classify the emotion expression at this low spatial frequency range (Bannerman et al, 2012).…”

The case for characterising type-2 blindsight as a genuinely visual phenomenon

“…There does seem to be converging evidence that, at least following injury to the developed adult brain, damage to V1 can eliminate the capacity to process information that might be necessary for making discriminations about contour, colour, texture, and figure-ground contrasts (Alexander & Cowey, 2010;Alexander & Cowey, 2013;Kentridge, Heywood, & Weiskrantz, 2007;Pavan, Alexander, Campana, & Cowey, 2011;Sahraie et al, 2010). If this is the case, then it is a very interesting topic for research that could lead to important insights about the phenomenon and the residual processing that subserves blindsight subjects' capacities.…”

“…Sahraie, Hibbard, Trevethan, Ritchie, and Weiskrantz (2010) have shown that DB's reported awareness depends on first-order (luminance defined) stimuli, despite the fact that he can perform above chance with second-order (contrast defined) stimuli in a forced-choice discrimination task (see Fig. 2).…”

“…Examples of (A) a sine-wave luminance-defined first-order Gabor patch and (B) a second-order contrast-defined stimulus (fromSahraie et al, 2010).…”