In class the concept of blindsight was explored after reviewing an inattentional blindness experiment (https://www.youtube.com/watch?v=vJG698U2Mvo). Individuals with blindsight have damage to their primary visual cortex (V1) and identify as blind even with residual vision. While they have an absence of visual awareness, they demonstrate appropriate responses to certain visual stimuli (most often in response to fast-moving and/or high-contrast visual stimuli). The primary explanation for this event is that retinal information is projected to subcortical structures and then projected directly to extrastriate regions, ultimately diverting V1. The exact process of blindsight however is unknown.
Blindsight can be explored to gain understanding of the connection between sensory areas and sensory awareness, as well as illuminate the organization of visual areas of the brain. Similarly, the phenomena of “deaf-hearing” can also be used to understand the relationship of the auditory system and of auditory awareness. Like blindsight, it’s important to recognize that there are multitudes of people, myself included, who are legally deaf but do not have a total inability to hear. Many have profound or severe hearing losses, some that can hear certain frequencies and sounds better than others or may be completely deaf in those areas. Brogaard (2017) refers to this form of deaf-hearing to be type-2 deaf hearing, because there is still “an ability to behaviorally detect or discriminate aspects of sounds that are not consciously perceived” (p. 23).
In this particular article (http://dx.doi.org/10.1080/09515089.2016.1268680) a profoundly deaf individual, LS, was examined with and without his hearing aids (without the accommodation he reported being unable to hear any sounds) by completing five trials. LS’s conductive hearing (volume at which a sound must be played through the ear for it to be heard; how hearing aids assist an individual) averages 95 dB which makes it a profound loss. As with most deaf people he suffers from tinnitus (the perception of imagined noise in the ear- I occasionally experience this as a repetitive ringing or droning sound), but the symptom generally does not have a perceived relationship with deaf-hearing. He also experiences vision-sound synesthesia in which a perceived sound is heard in response to objects in his environment. For example, the motion of objects corresponds to imagined sound that he has always associated them with (i.e. the sound of birds chirping when seeing them even if they can’t physically be heard).
The trials featured a series of forced-choice paradigms to measure sound detection, localization, and content discrimination. Each trial featured a hearing aid condition and hearing aid off condition, where LS served as his own control when wearing his aids. In the source localization trials without his hearing aids LS performed by chance and does not have “unconscious hearing” when determining the presence or location of sounds. When discriminating sounds however he performed above chance in this forced-choice model which means he has the ability and awareness to detect auditory content. It’s important to note though that the tinnitus may have served as a mask during this scenario. Although LS could not detect or localize sounds, he was able to discriminate among auditory content which offers an impressive outcome. The nature of deaf-hearing is still unknown and subject to many possible mediating variables, but the existence of unaware consciousness is undeniable.
*At the top is LS’s audiogram and at the bottom is mine. I included both of these to serve for comparison of how different our hearing is from one another, yet we still experience similar symptoms as a result of being deaf.
As someone who is deaf with a cochlear implant, this article was fascinating to read and offered many explanations about things I’ve experienced but never consciously recognized. I often find myself having conversations with friends and will accidentally say something they said immediately prior. I never ‘hear’ what they say, but I somehow parrot them word-for-word. I also learned about vision-sound synesthesia which I never realized that I had. While I still have about 10% or less natural hearing left in my non-implanted ear, I don’t hear every sound around me or I’m sometimes too far away from the source to properly hear it. Despite these obstacles, I am so used to associating specific sights with specific sounds that I ‘hear’ the sounds despite the impossibility of being able to do so. The trials in the article are also remarkably similar to my audiologist mapping appointments (when I get my implant sound frequencies readjusted after a period of fluctuation) in which I have to sit in a soundproof booth and acknowledge beeps and words with my implant on and off.
It was difficult to find many articles about deaf-hearing and like blindsight the concept is not well understood. As someone who experiences deaf-hearing and similar symptoms, it would be fascinating to learn more about the phenomenon in the future and further discover the relationship between sensory areas and awareness processing in the brain.
If you’re interested in learning more about this topic, another older, associated article is (https://doi.org/10.1016/S0010-9452(08)70837-2)