Cones are thought to be linked our explicit, decontextualised take of reality delivering our detailed impression of real settings in central/macular vision. Rods are then associated with peripheral vision and its specialisms of implicit spatial awareness and sensitivity of motion. However, although there are about 100 million rods across the retina they are considered to be 'saturated' in daylight conditions and responsive for night vision only. I would suggest that rods are actually optimised in daylight conditions and that we are missing the passive transmission of a specialised data potential. Could this be decoherence at work? A 'dark' data potential essential to the formation of perceptual structure?
Retinal Receptor Functions http://youtu.be/XzA7zirZK7s
There are two types of vision systems, one for photopic light levels (daylight, bright light conditions) an are subserved by cones and one for scotopic light levels (night time, low light level) due to rods. Rods have inherently higher sensitivity than cones (to the level of detecting individual photons) and hence under bright light conditions, they saturate. There is considerable evidence that the level of discriminabitlity is set by the dark noise or dark current of the rod system. A good book for you to read on this is by The First Steps in Seeing by Robert Rodieck
I do not think it is possible for a saturated receptor to deliver reliable information. And it is certain that rods are saturated in daylight. So I would rule out any daylight rod contribution to motion discrimination. Cones are especially linked to motion and spatial information thanks to the connectivity of cone bipolar cells (diffuse bipolar cells) and to the complex receptive fields of direction-selective ganglion cells that cone bipolar cells contribute to build. Certainly, amacrine cells also contribute to the formation of such receptive fields, but to my knowledge information are still not enough to propose a reliable model
Thanks for that Eugenio. However I read in many accounts, most recently in Eric Kandel's book "The Age of Insight' both that rods are saturated so are inoperable in daylight conditions and that 'the where pathway receives most of its input from the rods in peripheral regions of the retina and is specialised for the detecting motion and spatial information." So I think he is also suggesting the cones in the periphery assist with this as well of course.
Have you had the chance to look at the Vision-Space presentations? Its clear when we study the data-strcutures of phenomenal field that peripheral vison is essentially 'a field' structure and its this that provides the 'where' capability via proximity cues. We generate this field but it has to be populated by data from the 'where' pathway that must derive this data potential from the light array. This data-strcuture can have nothing to do with optical 'projection' reliant of the fundamentals of optics. So I propose that rods are actually delivering a noisy spatial data potential from which are able to penetrate (perhaps in the SC). This data structure would not be 'seen' by science as generated from linear spikes but by non-linear firing across areas of receptors that build in relation to other areas into an holistic awareness of space. The processes being akin to synthesis and not differentiation. If this is the case then we we might look to 'decoherence' for a physical explanation.
To get the retina the perform to the reception of this type of data potential we would need to expose it not to artificial (experimental) lighting conditions or video but real settings natural lit. i.e. situations the retina has evolved to encounter.
I just don't buy the inoperable saturated millions of rods story. I also don't think that the population of cones in peripheral areas could generate perceived spatial awareness. How often would we use the specialist rod facility at night? Are we especially spatially aware at night? I am not!
Dear John,
I do not know. I understand your point and indeed having so many receptors useless by daylight is unsettling. It still seems to me difficult to have discrimination among a population of saturated receptors. Besides, at the far periphery there is an increase in the concentration of cones (particularly on the nasal side of the retina) that could account for catching movements of objects entering the visual field. The thing is that you do not really see at the far periphery. You catch something moving and then you rotate eyes and head to align the foveas with the object. However, there is wide space for the debate and keeping an open mind is essential. Though I am skeptical, you are possibly running in a good and mostly unexplored field of research
I really appreciate your thoughts Eugenio. Have you had a look at the Vision-Space demos?
The structure of monocular vision http://youtu.be/AO71a8LzZSg
The incorporation of binocular stereo information http://youtu.be/xLY60lm86Mk
Process of information exchange within phenomenal field http://youtu.be/8hmgutPGJmQ
We have a software tool that takes in optical media (CG graphics) and transforms that into Vision-Space moving image media, both monocular and stereo. I think it gets close to modelling visual awareness. Imagine an object flying though the field structure as you were engaged in another act of observation in central vision. You would know 'where' it was 'implicitly'. Without looking at it and building up occlusion cues etc etc. Enough to ensure that the brain could adapt the shape of the lens to the correct focal length PRIOR to the ballistic saccadic eye movement. This is how its done of course! We have holistic sub-conscious spatial awareness to movement through the field and this promotes activity to central vision and conscious attention.
I am hoping that this approach to modelling visual awareness will encourage vision scientist to think about the end product! If we can describe the end product then we should be able to have a go at thinking clearly about how it gets there and what's involved. So Vision-Space is designed to be provocative in the hope that we could jointly establish an academic architecture for phenomenal field. I attach the full list of presentations. Please keep thinking about these issues!!!
I think there is an Elephant in the room - perceptual structure - the system that we as biological systems generate and into which sensory data is posted to be realised. Audition being performed in the same set-up?
This is kind of related
Vision-Space: What’s in an artificial stimulus? http://youtu.be/9ryFnuFCGys
Vision-Space suggests that we need to think very carefully about what we ‘mean’ by our stimuli. To what degree does the structure of the stimuli we feed into the visual system reflect prior beliefs we hold about vision? To what extent does the structure of our stimuli affect experimental ‘results’ and reinforce prejudice? Does the current structure of stimuli actually negate any pretence of experimental objectivity with respect to the system under investigation? Have we constructed a hall of mirrors? The answer to the question in the title is, our limited understanding.
Interesting article in Nature Neuroscience. Tamas Szikra et al. published online 26 October 2014; doi:10.1038/nn.3852
Title: Rods in daylight act as relay cells for cone driven horizontal cell mediated surround inhibition
As per usual I try to hammer Vision-Space into its set-up and findings!
If the rods are saturated then perhaps this is a function. Why evolve coultless millions of the things cover the retina with them for use only at scoptic light levels when we are all asleep! They are obviously ‘in use’ at photopic levels.
Evidence: 1. They mediate cone firing 2. They mediate ipRGC firing 3. Rods are thought to provide spatial awareness 4. We have determined a 3D disroder field and with it can model visual awareness.
So, saturation is a condition that needs to be present. It’s not null. A process is required to extract the signal? What contribution is this likely to be making to vision? Ans? 3D disorder field provisioning spatial awareness and proximity cues. We can articulate that and explore the attributes in Vision-Space. Potentially veridical. What’s required to extract any meaning from the situation at the retina?
Supposition: The saturation is the detection of background noise that in itself is useless. This has to be processed in conjunction with other inputs or influences. These providing a kind of ‘key’ to unlock the trace of a signal from the noise. That signal is still not going to ‘mean’ anything to us without further input from ‘us’. We have to give it a locus to form around. Fixation or ourselves (head). It's an active processing process! We are involved in it. We are integral to it.
This process would involve a good deal of feedback. Signal without environmentally conditioned noise will not activate the specialised processing system in a typical fashion. The system may be active but establish that there is no relevant content variation to monitor. All cells would record much the same thing and the response would be constant - meaningless in spatial terms. So: Conditioned white light without environmental conditioning would produce something like the above?
The function of rods in daylight conditions (photopic) is not to respond to changes in light intensity, its job is to record noise from which spatial information can be propagated. This process requires ‘key’s’ in the form of input from other cell types. Noise is seen in relation to….? Data from across the retina must then be compiled by us to manifest the meaning. This ‘meaning’ is holistic and implicit in nature not explicit and local. At low luminance levels (scoptic) there is a threshold where not enough noise is present to enable this process to continue to be productive and so the rods change their function and become sensitive to changes in intensity.
Interesting article in Nature Neuroscience: VOLUME 13 | NUMBER 9 | SEPTEMBER 2010
Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities Cara M Altimus1, Ali D Güler1, Nazia M Alam2, A Cyrus Arman3, Glen T Prusky2, Alapakkam P Sampath3 & Samer Hattar1,4
In mammals, synchronization of the circadian pacemaker in the hypothalamus is achieved through direct input from the eyes conveyed by intrinsically photosensitive retinal ganglion cells (ipRGCs). Circadian photoentrainment can be maintained by rod and cone photoreceptors, but their functional contributions and their retinal circuits that impinge on ipRGCs are not well understood. Using mice that lack functional rods or in which rods are the only functional photoreceptors, we found that rods were solely responsible for photoentrainment at scotopic light intensities. Rods were also capable of driving circadian photoentrainment at photopic intensities at which they were incapable of supporting a visually guided behavior. Using mice in which cone photoreceptors were ablated, we found that rods signal through cones at high light intensities, but not at low light intensities. Thus, rods use two distinct retinal circuits to drive ipRGC function to support circadian photoentrainment across a wide range of light intensities.
This is highly speculative but worth a punt? I apologise for the lack of a properly worked up painting but I'm brassic! (skint, broke, financially embarrassed, penniless!)
Vision-Space: Awareness is a dance mediated and augmented by ‘mind’ within a multidimensional space
https://youtu.be/-DCx5kLS2MQ
Amazing as it may seem I think that what the rods are contributing to at photopic levels is dealing with exposure challenges within the field of vision? Locally setting intensity levels so available of working detail is maintained?
As we look a scenes with varying luminance levels what we perceive is kept within a viable scope on a global basis by the aperture/pupil. However we also adjust locally. This ensures that valuable detail is not lost in shadow or bright light bleaching. Obviously there are limits to what can be done but it’s amazing how different a photograph taken with the right exposure looks to the experiential phenomenon. We see far more!
So the rods could be mediating/regulating the degree to which (not what) the cones report back at photopic levels. Through the mesopic scale we see the change over from mediation to a direct contribution to vision as receptors in their oven right at scotopic levels. The intensity regulator turns informer.
If this is the case we still have the missing contribution of spatially contextual (peripheral) vision at photopic levels?
I think this aspect/contribution to vision is an entirely different animal!
Camera design could learn from this?
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