Greetings,

I discovered this interesting rebroadcast while scrolling through several PBS Nova science episodes. Midway through, this specific episode profiled an experiment involving a subject who suffered a blind spot in her vision field due to a stroke that damaged a portion of her brain’s vision processing center. Despite that, an experiment during this Nova episode showed that this person was somehow able to perceive objects placed in her blind spot though seemingly not consciously aware of those objects.  For Nova commentators, this compelling paradox posed the larger question of whether there’s a need for consciousness when we may be quite able to perceive our environment without it. The answer, according to those commentators, may involve the importance of conscious awareness to infant learning--but that answer, in my view, completely ignored the question of why the subject in experiment was able to perceive objects without being consciously awareness of those objects.

Towards the end of this 30-minute Nova episode, its commentators focused on a blanket explanation that offered a perspective of how our brain stitches together our reality from very little information.  However, I generally find that the perspectives of brain function that these commentators and most neuroscientists agree with are flawed.  For example, most neuroscientists believe that the thalamus generally functions as neural relay station that filters what sensory information ultimately reaches the cortex where sophisticated neural processing occurs.  Until recently, I believed similarly but they and I were wrong.

Although I have a keen interest in neuroscience, I am not a neuroscientist.  However, what the overall evidence in science suggests to me now is that the thalamus functions more like a tuning fork during infancy that becomes more like a central alarm as we mature.  This distinction is important because it explains what may be happening in a brain that produces aberrant output and behaviors such as schizophrenia, autism, dementia, and perception in the absence of conscious awareness. 

As I perceive the evidence, our brain function comprises two structural components: the thalamus and everything in the cranial cavity other than the thalamus.  There may be maladies and physical defects affecting these components that can and do contribute to the aberrance our brain function may produce but understanding the precise functional role of these components--minus potential maladies and defects--is crucial to understanding and ameliorating the potential aberrance each component could produce.  I welcome your thoughts.

16 hours ago, DrmDoc said:

Greetings,

I discovered this interesting rebroadcast while scrolling through several PBS Nova science episodes. Midway through, this specific episode profiled an experiment involving a subject who suffered a blind spot in her vision field due to a stroke that damaged a portion of her brain’s vision processing center. Despite that, an experiment during this Nova episode showed that this person was somehow able to perceive objects placed in her blind spot though seemingly not consciously aware of those objects.  For Nova commentators, this compelling paradox posed the larger question of whether there’s a need for consciousness when we may be quite able to perceive our environment without it. The answer, according to those commentators, may involve the importance of conscious awareness to infant learning--but that answer, in my view, completely ignored the question of why the subject in experiment was able to perceive objects without being consciously awareness of those objects.

Being able to see without knowing is far less strange than being blind and thinking you can see...

8 hours ago, dimreepr said:

Being able to see without knowing is far less strange than being blind and thinking you can see...

Possibly apt, but decidedly amusing. However, I think the explanation for how a person may be able to perceive objects within a visual blind spot caused by brain damage is that the visual information for those objects are resonants of the thalamus that do not abate because they do not receive the visually interpretive/abating neural feedback from the damaged brain areas associated with such neural responses.  It’s analogous to sonar where a stimulated thalamus emits an information laden, neural ping into surrounding brain structures that don’t return an visually identifying, reciprocal hit because the structures associated with discerning that information has been damaged...but that doesn't suggest that surrounding, undamage structures are unaffected by that neural pinging nor does it suggest they are unresponsive.

I think the person in this Nova episode was able to correctly select the objects placed in her blind spot from among objects that were not because the objects she identified had the same or similiar resonant affect on her thalamus--they were correctly selected by how they made her feel rather than how they visually appeared.

Greetings,

Adding a bit more clarity to my last comment, visual experiences are likely processed in the brain in ways that are more than just visual. For example, if you know the instrument, we don't have to see a drum to identify it by it's percussive sound, feel or tactile outline with our eyes closed. What this suggest about the Nova experiment I described earlier in this discussion thread is that the visual information the participant in that experiment experienced likely resonated with the non-visual processing areas of her brain in a way that allowed her to correctly select which objects were place in the blind spot of her vision field--those correctly selected objects likely resonated with her in a way that was non-visual.

This is one time I would agree with Dimreepr.
Every healthy eye ball has a blind spot; I have blind areas due to Glaucoma.
A person with two functioning eyeballs uses the opposite eye to compensate for each eye's blind spot.
Unfortunately, I only see with one eye, but on a bright day I do have a little vision in my left damaged eye, such that I would see doubled yellow lines down the middle of the street. Eventually my brain learned to ignore the signal coming from my left eye, and my right eye became dominant, so I no longer see doubled up street lines.
In effect, the left eye's field of view became a brain blind spot.

Can the brain adapt ( plasticity is the term, I believe ) to pick and choose what it can or can't see ?

8 hours ago, MigL said:

This is one time I would agree with Dimreepr.
Every healthy eye ball has a blind spot; I have blind areas due to Glaucoma.
A person with two functioning eyeballs uses the opposite eye to compensate for each eye's blind spot.
Unfortunately, I only see with one eye, but on a bright day I do have a little vision in my left damaged eye, such that I would see doubled yellow lines down the middle of the street. Eventually my brain learned to ignore the signal coming from my left eye, and my right eye became dominant, so I no longer see doubled up street lines.
In effect, the left eye's field of view became a brain blind spot.

Can the brain adapt ( plasticity is the term, I believe ) to pick and choose what it can or can't see ?

It can, but I don't believe that is true regarding the Nova experiment. There’s a distinct difference between blind spots caused by damage to the eye only and those caused by damage to the optical cortex of the brain.  It’s a distinction between the photo stimulus impeded by damaged or obscured photoreceptors and unimpeded stimulus that actually traverse our optic nerves through the thalamus into brain structures.

That Nova experiment targeted a blind spot caused by brain rather than eye damage with test objects placed in a fixed field of blindness unobservable by the other unaffected eye.  I believe that experiment proved that our visual experiences impact us in more ways and on more levels than those that are visual.  That impact clearly doesn’t radiate from the visual cortex, it radiates from the core of brain structure, which is the thalamus.

I have not seen that episode, but was it about blindsight? I.e., damage in the primary visual cortex that removed the ability to consciously perceive things, but unconsciously processed them (e.g. in form of avoiding objects or reflexively react to movement)? There have also been variations thereof, where they for example cannot perceive color, but notice differences in wavelengths.

I remember having read about that a long time ago during undergrad and was immensively fascinated by those studies. It was presented IIRC as a way how the brain does parallel processing of cues at various levels rather than in neat distinct areas. Though I am not sure if additional studies have changed that view since then.

20 hours ago, CharonY said:

I have not seen that episode, but was it about blindsight? I.e., damage in the primary visual cortex that removed the ability to consciously perceive things, but unconsciously processed them (e.g. in form of avoiding objects or reflexively react to movement)? There have also been variations thereof, where they for example cannot perceive color, but notice differences in wavelengths.

I remember having read about that a long time ago during undergrad and was immensively fascinated by those studies. It was presented IIRC as a way how the brain does parallel processing of cues at various levels rather than in neat distinct areas. Though I am not sure if additional studies have changed that view since then.

With one sentence, you've masterfully conveyed thoughts I've struggled to express over several previous posts. It was apparent to me that the Nova participant's brain was parallel processing more than visual cues from the objects she correctly selected. This appears to suggest that her brain was receiving more stimulus from those objects than what might affect that portion of her visual cortex if not damaged. Therefore, she was clearly conscious of something because, as I believe, even our unconscious reactions require a coordinated and focus response from brain function to execute those reactions. I'm suggesting that it's the function of our brain's core (thalamus) that makes these reactions possible.

As I said previously, I don't believe the thalamus is a kind of neural relay station and I don't believe it has the capacity to filter the afferent flow of sensory it receives. In fact, I believe it lets everything about our experiences into every area of the brain and the stimulus that's most impactful on those areas is what receives a focus response--conscious or otherwise.

Edited April 23Apr 23 by DrmDoc

55 minutes ago, DrmDoc said:

As I said previously, I don't believe the thalamus is a kind of neural relay station and I don't believe it has the capacity to filter the afferent flow of sensory it receives. In fact, I believe it lets everything about our experiences into every area of the brain and the stimulus that's most impactful on those areas is what receives a focus response--conscious or otherwise.

So I vaguely recall that maybe around 2000ish I found some papers discussing the role of the thalamus in blindsight and that because of what they find they are postulating different types of it. I am moderately sure that I put it at least one of those on my to read pile back in my office. Maybe I can find those papers online again (or maybe they are overturned at this point).

On 4/23/2026 at 5:27 PM, DrmDoc said:

,,,I believe it lets everything about our experiences into every area of the brain and the stimulus that's most impactful on those areas is what receives a focus response--conscious or otherwise.

Just to clarify this bit, I don’t perceive thalamic function as letting in everything as if an open door. I perceive that function as more akin to a tuning fork or bell that, instead of sound, continuously emits neural impulses into surrounding brain structures upon impact of sensory stimulus.  From my perspective, stimulus data arrives in unfiltered waves of neural impulses from the thalamus to our cortex and it is our cortical responses or lack of response to that data that defines our perceptions or behavioral output as filtered or unfiltered.

Rather than a result of some sophisticated neural process, from my perspective, our cortical responses are little more than a type of neural noise suppression or reduction process comprising equivalent neural frequencies manifesting our behavioral responses--as similarly suggested by a toddler's response when asked to repeat a phrase, which the child may do to accomplish little more than to end the asking.

19 hours ago, DrmDoc said:

Just to clarify this bit, I don’t perceive thalamic function as letting in everything as if an open door. I perceive that function as more akin to a tuning fork or bell that, instead of sound, continuously emits neural impulses into surrounding brain structures upon impact of sensory stimulus.  From my perspective, stimulus data arrives in unfiltered waves of neural impulses from the thalamus to our cortex and it is our cortical responses or lack of response to that data that defines our perceptions or behavioral output as filtered or unfiltered.

Rather than a result of some sophisticated neural process, from my perspective, our cortical responses are little more than a type of neural noise suppression or reduction process comprising equivalent neural frequencies manifesting our behavioral responses--as similarly suggested by a toddler's response when asked to repeat a phrase, which the child may do to accomplish little more than to end the asking.

This seems related to something I've been pondering for a while; pigeon's are capable of dodging a peregrine at full throttle, having seen them within meters.

We only have so much time to process reality, and our primary sense takes priority.

On 4/25/2026 at 12:19 PM, DrmDoc said:

a type of neural noise suppression or reduction process comprising equivalent neural frequencies manifesting our behavioral responses

Curious to explore further what the source of that ambient / background noise in the system might be or where it comes from in your opinion.

Waves of nearly all varieties tend toward stillness... the waves ripple until tiny enough to be gone / turn to heat. In the neural system, likely this would be the same were it not for incoming stimulus... internal stimulus too... but somewhere there must be a "rock" getting dropped into the "pond" creating the initial ripple.

Struggling to put words to my question without venturing into the abstract, but the noise being suppressed... where might that come from / what might be the source of that?

Okay if you don't know. Just putting out there a question which arose for me as I read your update above.

On 4/25/2026 at 11:19 AM, DrmDoc said:

Rather than a result of some sophisticated neural process, from my perspective, our cortical responses are little more than a type of neural noise suppression or reduction process comprising equivalent neural frequencies manifesting our behavioral responses--as similarly suggested by a toddler's response when asked to repeat a phrase, which the child may do to accomplish little more than to end the asking.

I think a problem with that explanation is that it is mechanistically vague. The issue of course is that (at least when I read about it) the mechanisms themselves are not really known, and might still not be. A focus at that time was on the better understood elements, such as the anatomy of connections, thus following the potential pathways of information. The attractive element is that in both structures there are areas that directly map the visual field, which makes objective tracking of visual areas feasible. The big issue is that this phenomenon breaches the area of subjectivity and consciousness, where it is much less understood how neural correlates create the subjective awareness.

From what I remember, early focus was on on connections that bypass V1 and therefore create an attractive anatomical model of these other circuits that add up to our total perception of things. Going back to the idea of a tuning fork- from what I remember I think this might be a bit of an overstatement, or at least it might require qualification:

On 4/25/2026 at 11:19 AM, DrmDoc said:

From my perspective, stimulus data arrives in unfiltered waves of neural impulses from the thalamus to our cortex and it is our cortical responses or lack of response to that data that defines our perceptions or behavioral output as filtered or unfiltered.

It might be a matter of how we define data but even on the sensory layer, stimuli are heavily modulated and the anatomic structure and connections themselves are doing a lot of filtering and signal modulation. In that model it seems that the thalamus is an extension of that? I.e. the distinction would be more of amount of filtering rather than being filtered and unfiltered (as anything leaving the sensory would be processed somehow).

Very, very vaguely I think I had a discussion with a prof back in the days about the role of the thalamus as a signal relay and that how the signals are distributed (I suspect that is what you might mean with tuning fork?) could affect how the signals are then subjectively perceived. One could argue (and I am fully speculating here, based on vague decades-old memory), for example that some might for example have motor-relevant information, but depending on how the signals are routed, (the way I imagined was a splitting of signal across different pathways) some elements get suppressed in terms of conscious perception, others are heightened. The former could trigger motor responses by suppressing or delaying slow, conscious processing (e.g., if you need dodging something). And subcortical structures such as the thalamus can be themselves be tuned to send signals one way or another (e.g., if you are relaxed vs fight and flight mode). But again, this is really not even a student-level explanation as I have really stopped reading on this field a long time ago, to some regret.

On 4/27/2026 at 9:40 AM, iNow said:

Curious to explore further what the source of that ambient / background noise in the system might be or where it comes from in your opinion.

Waves of nearly all varieties tend toward stillness... the waves ripple until tiny enough to be gone / turn to heat. In the neural system, likely this would be the same were it not for incoming stimulus... internal stimulus too... but somewhere there must be a "rock" getting dropped into the "pond" creating the initial ripple.

Struggling to put words to my question without venturing into the abstract, but the noise being suppressed... where might that come from / what might be the source of that?

Okay if you don't know. Just putting out there a question which arose for me as I read your update above.

An interesting question, but what I perceive may not be as abstract. If we think of the thalamus as an organ that transmutes sensory afferences into neural impulses equivalent to varying tonal waves and frequencies, then surround brain tissue would be those structures with an affinity for the distinct tonal characteristics or measure of each neural wave and frequency.  The job of those surrounding structures would be to generate neural feedback sufficient to initially match then mute or suppress the effects of those distinct neural tones at their source. In the brain, that neural feedback from surrounding structures transmutes through the thalamus as behavioral output addressing the source of a stimulus.  This, as I envision, is what produces the behaviors toddlers exhibit when, for example, learning language—all they appear to understand initially is that mimicking what they’re continuously asked to say is frequently sufficient to suppress the asking.

Addressing your analogy, the rock would be the sensory stimulus, the pond would be the thalamus, and the shore would be the surrounding brain structures. The difference would be an endless ripple onto shore by that single rock until met by counter wave energy from the shore.

On 4/27/2026 at 4:49 PM, CharonY said:

I think a problem with that explanation is that it is mechanistically vague. The issue of course is that (at least when I read about it) the mechanisms themselves are not really known, and might still not be. A focus at that time was on the better understood elements, such as the anatomy of connections, thus following the potential pathways of information. The attractive element is that in both structures there are areas that directly map the visual field, which makes objective tracking of visual areas feasible. The big issue is that this phenomenon breaches the area of subjectivity and consciousness, where it is much less understood how neural correlates create the subjective awareness.

I agree, we should focus on what we know and that should probably begin with a primary imperative of brain functions, which is homeostasis. Although we currently understand the thalamus by little more than its circuitry and mapping, it's clearly the structural core of the brain and, thereby, the core of brain function. Whatever affects the thalamus should also affects brain function and its functional imperative. We know there's more than sufficient evidence suggesting that what happens in the cortex is secondary to thalamus function and its that secondary activity that produces our behavioral output.

We know that our sensory experiences impact thalamic function and that impact transmutes as neural impulses that initiate a cascade of recipricol cortical neural responses sufficient to address that sensory impact. On a neural basis alone, this is the equivalent of the brain producing sufficient neural feedback to suppress some homeostatic destabilizing neural effect. It's that neural feedback that carries our behavioral responses to sensory stimulus.

On 4/27/2026 at 4:49 PM, CharonY said:

From what I remember, early focus was on on connections that bypass V1 and therefore create an attractive anatomical model of these other circuits that add up to our total perception of things. Going back to the idea of a tuning fork- from what I remember I think this might be a bit of an overstatement, or at least it might require qualification:

It might be a matter of how we define data but even on the sensory layer, stimuli are heavily modulated and the anatomic structure and connections themselves are doing a lot of filtering and signal modulation. In that model it seems that the thalamus is an extension of that? I.e. the distinction would be more of amount of filtering rather than being filtered and unfiltered (as anything leaving the sensory would be processed somehow).

I agree; I think of filtering as what one might do with an air or water purifier, I don't think that's what the thalamus does. I don't think the evidence suggests that any processing occurs in the thalamus other than to transfer sensory stimulus to destined cortical structures in continuous unfiltered waves of neural impulses until suppressed by recipricating waves from the cortex albeit via defined neural circuitry from well-studied structures.

On 4/27/2026 at 4:49 PM, CharonY said:

Very, very vaguely I think I had a discussion with a prof back in the days about the role of the thalamus as a signal relay and that how the signals are distributed (I suspect that is what you might mean with tuning fork?) could affect how the signals are then subjectively perceived. One could argue (and I am fully speculating here, based on vague decades-old memory), for example that some might for example have motor-relevant information, but depending on how the signals are routed, (the way I imagined was a splitting of signal across different pathways) some elements get suppressed in terms of conscious perception, others are heightened. The former could trigger motor responses by suppressing or delaying slow, conscious processing (e.g., if you need dodging something). And subcortical structures such as the thalamus can be themselves be tuned to send signals one way or another (e.g., if you are relaxed vs fight and flight mode). But again, this is really not even a student-level explanation as I have really stopped reading on this field a long time ago, to some regret.

No regrets: the thalamus has been my obsession for quite some time and it's maddening...but it has led me to avenues of understanding I've never previously considered.

Thanks for the thoughtful answer.