Pioneers of sight

 Watching a hawk circle the canyon overhead starts out as packets of light or ‘photons’ striking my retina. How these photons strike the retina and which pathways they activate in the brain tell me what I’m seeing. Photons landing in a specific orientation will travel pathways that construct its’ form (bird). When they hit adjacent areas in succession I’m informed of its’ motion and direction. And the length of time between hits tells me its’ speed. None of this was known before 1968 when David Hubel and Torten Wiesel first announced their research findings. And it wasn’t until 1981 that it was generally accepted and they earned the Nobel Prize in Neurophysiology and Medicine.

Resource-based attention

In an elegant ‘simulation’ of economic-class differences, researchers found that people with means (those in higher economic classes) don’t have to focus so much on their immediate needs and are more likely to consider the future cost of borrowing when making purchase decisions. On the other hand, people with limited means, who do have to focus on immediate needs, make better use of the resources they have but lose sight of the future cost of borrowing. As a result, they are more likely to become over-extended [ link ]. This means that no matter who you are, having limited resources alters the way you perceive and make borrowing decisions. They simulated economic differences by altering either the amount of time or the number of opportunities each group had available to make choices. The group with less time made better use of it when making purchase decisions than the group with more time. However, when they were allowed to ‘borrow time’ from future periods, at exorbitant cost .. these advantages diminish. This tells me that it’s not some innate ability to defer gratification that distinguishes rich from poor. When you have less to spend ..your attention is, by necessity, focused on the demands of the present situation.

Refreshing the mind

EEG recordings from the visual cortex show that conscious experience is ‘periodically refreshed’ rather than ‘continuously updated’. Sensory memory persists long enough to bridge the gap [ link ]

Expectation-based perception

The journal Nature reports that expectation of a sensory event can increase the speed and accuracy we perceive it [ link ]. “Animals are not passive spectators of the sensory world in which they live. In natural conditions they often sense objects on the bases of expectations initiated by predictive cues. Expectation profoundly modulates neural activity by altering the background state of cortical networks and modulating sensory processing” [ link ].

Expectations alter perception ..I know this from my own practice. Expectations amplify and channel speech perception. Listeners have to take a moment to adjust when speakers say something that defies expectation. This study shows that the same holds true for taste. In one sense experiences arrive one by one, always fresh and new, but over time they become familiar re-enactments of prior experience. For instance I like yogurt for breakfast ..so I say it’s good and look forward to it when I get up in the morning. Good is a property I supply as something I experienced so long ago I don’t remember. It’s no longer fresh and new but an experience that my expectations enhance.

Sensory integration

This garden universe vibrates complete. Some we get a sound so sweet. Vibrations reach on up to become light, and then thru gamma, out of sight. Between the eyes and ears there lay, the sounds of color and the light of a sigh.  ~   Moody Blues

   

A recent study shows that baboons can learn to tell the difference between word and non-word strings [ link ]. In an accompanying editorial, Dr Michael Platt says this evidence suggests dyslexia might be more of a visual problem than a problem matching sounds to letters. It’s a rare opportunity that I get to hear a neuroscientist jump to an either-or conclusion like that. Reading is an integrated process that coops many areas of the brain. A problem in the visual system can produce a reading deficit just as profound as a problem in the auditory system. These systems are integrated by higher centers of the brain during reading. What these investigators discovered with baboons is a better example of pattern recognition. It’s a process shared by any species that survives in the wild. Over time, the visual system is tuned to distinguish what’s meaningful from what isn’t by a process of ‘statistical regularity’. Statistical regularity simply means that certain signal combinations appear more frequently with meaningful objects than with non-meaningful objects. It’s no surprise that a baboon can perform this with a string of letters just as easily as it can a set of racing stripes. And I have no doubt that humans require a working visual system as well as a sound system to be able to read coherently. The written word hasn’t been around long enough to evolve an area of it’s own in the brain like it has for speech and vision.

 

The bell jar

Conscious experience is a bell jar shaped by historical and environmental forces. What we call ‘ordinary experience’ is fashioned by exposure during early childhood and a sensory-network that has evolved over eons of earthly habitation. Recent findings published in the journal Proceeding of the Academy of Sciences help support my bell jar theory. They show that the sensory world is tuned by exposure early in life. Children growing up in cultures where their diets don’t offer much in the way of sugar, eventually lose the taste-receptor for it [ link ]. In the same way, children growing up in cultures where their language doesn’t include sounds found in other cultures eventually lose the receptor sites for them [ link ]. The neuro-pathways for discerning phonemes that are not available in the child’s early environment get ‘pruned away’. For example, children in Asian cultures that don’t have phonemes for the English ‘L’ and ‘R’ lose the ability to hear any difference between them.

Rhythm of the senses

The way information flows through the brain mediates the way we perceive the world. And an important property of information transmission is rhythm. Like a metronome, nerve cells in the brain display rhythmic activity. If one area changes it’s beat, in response to variations in external conditions, other areas adapt by changing their beat as well. This helps explains how perception changes faster than nerve signals change pathways [ link ].

The development of appetite

It’s well known that the ability to perceive the sounds of language is tuned in childhood as a result of the interaction between exposure and early development. Infants start out with equipotential for languages. However, by the end of the first year ..neural-pathways responsible for discerning the sounds of their native language get established. Turns out that appetite for particular foods are formed this way a well, perhaps even earlier inside the womb. Infants start out indifferent to tastes, however “..later exposure changes the way taste signals are carried to the brain.” Recent studies show how exposure to a diet of crackers, cereal and bread during early development results in a lifelong preference for starchy-salt rich food [link].

Immateriality

“Each person is capable of perceiving infinitely more. The universe is funneled through the reducing valve of the brain and nervous system ..what comes out at the other end is a measly trickle.”

From ‘The Doors of Perception’ by Aldous Huxley 

Only 20% of available ‘matter’ - at home or in the universe - is observable by the senses. This includes the composition of our bodies as well as all it’s surroundings. The remaining 80% is not even visible using the most sophisticated instruments of science. It’s a mystery supplied by indirection and the divinity of inference. What does this mean ..? Ordinary reality represents only a fraction of the energy that exists in the universe. The forces at work in my life are largely invisible. Perhaps the limits to what I can see are not so much physical as they are mental, like Huxley said.