Big Think Interview With Marcelo Magnasco

A conversation with the head of the Laboratory of Mathematical Physics at Rockefeller University
  • Transcript


Topic: The Eclipse in the Odyssey

Marcelo Magnasco: Back at the beginning of the century an astronomer named Carl Schoch decide to try to date a passage in the Odyssey that has been interpreted by many since classical times explaining the description of an eclipse. It’s a little bit of a difficult passage to try to interpret this lunar eclipse because the passage takes place indoors and the suitors who are supposed to be seeing this omen do not see it. But otherwise the description of an eclipse by Carl Schoch is very ****. So Carl Schoch tried to date this eclipse and he found that the only possible date would have been April 16, 1178 BC, which could agree rather well with the classical estimates of the Fall of Troy around 1190 BC okay the last ten years it takes for Odysseus to get back. We took these and we said okay if this is the only evidence that you find then the Odyssey is just a social story right; you can it’s neither here nor there right, what are you gonna do. You can’t corroborate it by any means just looking at the tapes. However, in the Odyssey there’s plenty of other references to things that happen in the sky. There’s a reference to Odysseus navigating by the stars, there’s a reference to seeing Venus high in the sky and so what we did was we set aside the eclipse reference and we just took the rest of the other references and looking at all those other references we found that because each one of them happens frequently but in combination all four of them would happen very rarely we were able to say that the only date compatible with these other references was also April 16, 1178 BC. So this gave us what we believe is a fully independent confirmation that on that date might be the date that’s actually inscribed in the Odyssey.

Question: What type of eclipse was Homer describing?

Marcelo Magnasco: Yes so the eclipse being described would be a total solar eclipse lasting a few minutes as they typically do and the narrative takes place at noon so that’s an important data and eclipses are very short and they are seen over very sort of, total solar eclipses are very short and they are seen over a very small swath of the earth because the size of the moon and the size of the sun are the apparent size of the moon and the sun are so near identical that when the moon covers the sun you have to be exactly at one given position and it doesn’t last very long so the description would be compatible with a total solar eclipse. The description says that it happens at noon, indeed the 16, April, 1178 BC eclipse happened close to noon time local time over the Ionian Islands so yeah in addition that particular eclipse would have been pretty impressive because you had all of the planets, all of the visible naked eye planets all of them simultaneously in the sky in a relatively small fraction of the sky as the eclipse happened so it would have been a pretty impressive, pretty impressive anomaly.

Question: Are your findings at all related to the use of the term “wine dark sea?”

Marcelo Magnasco: We haven’t. There has been a huge debate that I haven’t followed in all of its intricacies regarding the Dark-Wine Sea so at some point there was an idea that Wine at the time was way too strong to be drank without diluting and unless you diluted it it acquired some discolorations that looked like the sea. There has been an entire thread of people looking at that. It doesn’t help that we really don’t know exactly from the Homeric language. Some of even the words are still under dispute exactly what they mean. Clearly, Wine-Dark Sea is not something that we would call today the Sea okay but we don’t have the same wine today as they had in those times so I really don’t know about how to interpret that. What I can say on the other hand is that whenever you read the description of saline the description is extremely vivid in exactly you know how they have the masts, how they you know, how they pulled the ropes. The person writing seems to know very, very well what he’s talking about so clearly if you know if they are describing the sea as being you know wine in coloration probably their wine was indeed the color of the sea or something like that.

Question: How do we distinguish between noise frequencies?

Marcelo Magnasco: Okay so hearing is a difficult sense to understand on the theoretical viewpoint because it is pretty much unlike the other senses in many, in many relevant ways. So for instance we have in both our retinas we have about two-hundred million photo preceptors so each one of our eyes is a hundred mega-pixel camera. We have about a hundred million oral factor receptors in our noses. We have well over ten to twenty million for touch and for pain and for temperature on our skin yet the total number of auditor receptors we have in both of our cochlear is something like seven to eight thousand so there is a miniscule amount of cells that are being input from sound and therefore the nervous system really needs to extract as much information as it can from every, each one of them okay.

The information density being coerced out of each one of these detectors is much higher so it puts a lot of demand on the capability of the nervous system to process information. In addition, we do not have understand very well sound exactly the geometry of sound is in the sense that we can understand vision. We hear some words okay we hear a few seconds of phonings and these give rise to a multitude of very different percepts in your brain so on one side one stream you get out is the actual text being spoken. Then you also hear the accent of the speaker, the emotional stance of the speaker, many features related to the identity of the speaker if you know somebody you can easily recognize their voice but even if you don’t know them you immediately know whether it’s male or female, a child, and so on and so forth. All of these are impressions that are sort of separated by the brain into different persons that do not go with the same stream so it’s sort of difficult to try to understand in a unified sense what is it exactly that our hearing does.

Then there is all the spatial aspects of hearing that we normally attribute to our sight but actually, a lot of them are derived from hearing so when you hear somebody speaking you know perfectly well if they are talking towards you or towards a wall. You know whether they are turned around or not simply because of the muffling that would happen if the speaker is, is looking away from you. You know the position of the speaker with a fair amount of accuracy. We have very precise models in our brain of how the human voice sounds when you are yelling or when you are whispering and of course then there is an **** measuring the volume of the sound of the ear so you can distinguish whether somebody’s whispering in your ear from somebody shouting far away even though the volume of the ear would be precisely the same simply because you can interpret whether the pattern of the sound is that of a stressed voice stressed because of shouting or the muffled sound of somebody whispering.

You also have a clear impression of the space in which the conversation takes place; this is for instance the very space I’m in is very quiet space because echoes have been suppressed but not entirely. You have an impression for instance everybody is probably familiar with somebody in their house calling them from a different room and from the sound of the voice knowing exactly which room they are. Okay if somebody calls you from the bathroom you recognize that the shininess in the bathroom walls. You would recognize the more muffled sound of somebody calling you from the bedroom where you know the mattress and stuff absorb the sound. So there are all these variety of different percepts and so it’s sort of difficult to try and integrate auditory status into single category because the brain itself is separating different areas of the source and different areas of the space in which the communication is taking place in a very rapid and dramatic fashion.

Question: Do you work with music imagery at all?

Marcelo Magnasco: No we keep yes, we keep an interest in human perception of fairly complex and sort of idiosyncratic sounds like perception of music and the like because that’s ultimately what we are interested in understand, how human beings understand their world right. But we need to simplify our space of hypothesis and so there has been historically in new science studies a little bit of tension between extremes in sensory research. In one you try to present a subject and experimental animal a person with extremely simplified stimuli like in vision it would be just a dot of light, a single line, a grating a regular spacing of bars or something like that. These are extremely abstract stimuli but on the other hand they are very easily described mathematically in terms of a very small number of perimeters so if I’m describing to you a dot of light, it’s only attributed to a position, horizontal and vertical position and so on. Therefore the approach has a lot of power in trying to see if a particular neuron in my brain or in the brain of an animal responds to dots of light. Does it respond specifically to dots that happen in a specific location? Then it’s relatively easy to go and reconstruct exactly what is it that’s causing these neurons to respond okay. On the other hand the stimuli are extremely artificial, they are unrelated to the forces that shape the evolution of the brain, and it has been extremely difficult to try to put together much more complex sense from this very simply evidence. So if we try to study then how neurons in the brain respond to combinations of lights the number of perimeters blows up so rapidly that it has proven very difficult to get a lot of insight out of the root of building the world you know one line or one simple element at a time.

Another school of thought yeah sure so another school of thought has said on the other hand let’s try to do what the brain is supposed to do; the brain wasn’t evolved so that we could recognize dots and lines the brain was evolved so that we could recognize our predators, our prey, our mates in the context of a natural visual scene like a woods or something like that so how do we recognize the presence of one of our predators? Do we see a lion among the leaves? How do we find our mates? These are very complex natural scenes but this is what the brain was evolved to do so people have said okay let’s look at what characterizes these natural scenes as oppose to random television snow which is the most random possible stimulus okay.

What characterizes the very structured scenes of the natural world? Unfortunately those scenes are uncontrolled mathematically speaking namely, you go out in the wood and you make a film and you present it to your subject and you see whatever your neurons respond to but you do not have the power that you had in the previous approach of these very tight mathematical descriptions. So what we’ve been looking for in the auditory world is to try to find sounds that are natural but that are ecologically relevant to the given animal in the sense that being a sound that an animal has been evolved to recognize and to find or flee from and that we can describe in mathematical terms in very close form. And we have been study what we call Auditory Textures. These are sounds that occur sort of in a steady state so that one piece of the sound sounds quite like any other piece of the sound.

For instance the sound of running water you’re next to a brook you hear **** and you hear that sound continuously and if you record it for an hour the first minute and the last minute they sound exactly alike. The sound of fire, a fireplace cracking that’s a very nice, steady sound, which is statistically homogenous so you can look at one part, another part and nothing has changed. Or you know the sound of flies buzzing in the air or any other you know natural sound that has this you know this consistency and then we tried to take these sounds and abstract them so that we can describe them and resynthesize them computationally with the minimum possible number of perimeters.

In the case of water, we have found a remarkable way of actually synthesizing a very accurate sound of running water with only three perimeters, making it virtually as low-dimensional as mathematically tightly controlled as one line on a blackboard so and this approach then you know is trying to unite the power of you know the low-dimensional description of the simple stimulus with using a very natural and ecological and relevant sound like the sound of running water. Ever living being needs to be able to recognize water and go and find water or run away from water in case of flight so these are sounds that the brain was evolved to recognize very, very efficiently and this is where we stand with we’re studying, we’re trying to study how the brain recognizes these classes of sounds and how we can parse them and categorize.

Question: Does sound influence what we see?

Marcelo Magnasco: Yes indeed so in fact we believe that we attribute internally to vision most of our understanding of the space around us but a lot of it happens because of an auditory construction is linked to the vision reconstruction and it this process begins as early as a newborn who will turn their head towards the sound of their mother’s voice looking for her face. Now in experiments in which you present a subject in darkness with a flash and a click of sound coming from the same place and you ask them okay please point to the place where it happened, if you move away this auditory source of the click and the flash but they still happen simultaneously but in a different place the person still perceives them as being a single source as being a single object and they will point to a point in between that the flash and the sound of the click which is roughly one-third of the you know towards the light and two-thirds towards the click meaning that internally the brain is using both the evidence from hearing as well as the evidence from vision to try to reconstruct the location of that particular event and its roughly waiting vision twice as much as hearing but this is you know relatively surprising. We would think that actually we see the precise place where things happen and we sort of hear you know something very broad but it is not so. Our hearing acutely helps us to have a very detailed imagery of the world and again coming back to my previous point this is surprising because the amount of primary sensory receptors that are used for hearing is so much smaller than the ones that are used for vision that there is a substantial amount of information processing that the nervous system divulge to coerce this information out of the auditory stream.

Question: Have any of the senses had a more profound evolutionary significance?

Marcelo Magnasco: I wouldn’t say that of our senses is more powerful than the other. All of them are necessary for their own intended purposes right. So vision has certain special attributes. It’s very high resolution in the amount of information it conveys to the brain per unit of time. It also requires the brain to really interpret the scene it’s looking at in ways that requires an amount of time. Hearing is closer to the sense of smell in having a privilege connection to the motions. It’s much more easy to have a sound that changes our emotional stance than to have a visual scene that changes our emotional stance. And it’s sort of much more automatic right everybody is familiar with the calming sound of rain on a roof top or the alarm that the roar of lion will give you so you know it’s very common to go to the zoo and see the kids you know looking at the lion and then the lion roars and all of the kids go scampering out okay because looking at the lion is much more of an intellectual thing than actually hearing the roar of the lion that the brain has been evolved to actually fear and that’s why we actually use alarm clocks to wake us up. The hearing sense is on all the time right. We recognize sounds as we sleep and they will wake us up from sleep if need be. so they serve very different purposes all the senses right. I believe it was Helen Keller who was both blind and deaf that said that blindness separated her from things while deafness separated her from people and that of the two senses the most devastating lack was the lack of communication with other people so this is one of the ways in which you can see that the senses really have different use and different power.

Question: What are some of the difficulties in understanding memory?

Marcelo Magnasco: So if you think of memory you know memory is an all encompassing term going from just being able to integrate the last few hundred milliseconds of your sensory experience together that requires memory right because that few hundred milliseconds a second is longer than the direct memory of most neurons, it requires integrating everything in an intermediate structure which is you know shorter memory. There’s many different forms of memory and it’s I stalled here right, its, it really is an all-encompassing word in that we call memory very, very different things. My interest of the theoretical level in memory has to do with the lack of theoretical models for what we can normal memory namely we have fairly good artificial neuro models for in place of associations or for you know increased recognition of categories and the like so if we show a number of examples of a category or a number of examples of currencies, we can build artificial neruo networks, these are part of the computation structures okay which we run on the computer that look at these categorizations and eventually learn from the presentation of examples how to you know how to categorize things. So that we know how to do but in common language memory is a very thing and in common language basically everything I remember happened to me exactly once. It wasn’t like you get this many different examples and you categorize from them and you recall very vividly instances that happen to you like I said precisely once. So I remember vividly the birth of each one of my children. I do not have the same category called birth of children; I recall each one of them. I recall my first day of school it happened to me just once. Well I recalled my first day of elementary school and I recall my first day of high school okay and I recall them as two different instances not as two examples of first days of different schools all right. So we do not have much by way of a theoretical understanding of how the brain could do this okay we don’t have very well developed models of sort of a neuro network taking all of these data from the world and assembling them I mean to some into some coherent thing we called the memory whereby if we recall it we remember things that happened on one specific occasion that we saw precisely once right so that’s an interest I have about that I have to say that you know we don’t have currently a lot of results in the subject.

Question: Is it really true that we only use 10% of our brains?

Marcelo Magnasco: I should really research the origin of the ten percent of the brain meaning which is widely repeated many places. I don’t know exactly what the original statement was referring to but probably it was referring to the fact that the neurons in the brain, the neurons in the cortex of the brain fire sparsely in the sense that they are not active all the time sending electrical impulses, they fire at much lower rates than their you know than they would be capable of otherwise and but this does not mean that they are not in use all the time. Namely a neuron being silent means something as opposed to not meaning anything and therefore I really have no idea what it would mean to say we are only using ten percent of the brain. As far as the way anybody uses most of their brain most of the time, you know I don’t know exactly how

Recorded on: February 5, 2009