Here's a little essay I entered into the essay competition hosted by the Wellcome Trust and New Scientist:
The legendary captain Rhodri Raven yells from quarterdeck to his trusty buccaneers: "Scoundrels, fetch me the Treasure Map! 'Tis torn to four pieces, they say, cast by the winds upon the Occipital Isle, about the Calcarine Fissure cleavin' it across." Forty pirates dash to set sail, fearing their chief's temper, one eager enough to cut another Calcarine across those imprudent enough to disobey. But there's a problem... each pirate returns bearing one piece of map. "The map, not maps, I said", Rhodri growls, "Hand me the real one!" Yet they all look real...
These metaphoric maps stand for the various brain areas involved in vision. They are topographically structured, reflecting the organisation of the visual field on our eyes' retina, resulting in "retinotopic" maps drawn upon our brain's cortex. Each map is broken in half across our brain, with our left hemisphere processing information from our right field and vice versa. Furthermore, some of these half-maps are further broken into sections representing the upper and lower quadrants of our vision, such that we end up with four pieces adding up to each single map.
Researchers have charted numerous cortical maps, by using functional Magnetic Resonance Imaging (fMRI) to explore brain activation in response to stimulation of different parts of the visual field. Sixteen whole visual maps stretch from the Calcarine sulcus, in the Occipital lobe, at the back of our brain, to our prefrontal cortex, appearing grouped into different clusters, as islands aggregate into archipelagos. Our captain's question is inevitable: which one of them is real indeed?
In fact, they are all real, resulting in a cardinal problem for visual neuroscientists, understanding how perception depends on each of them: Does each serve a distinct goal and, so to speak, lead to a different bounty? And how is their content integrated into our seemingly unitary perception, into one vision?
Indeed, we know that some of the earlier maps contain information about the details in our visual world, breaking it up into edges, colour and motion. But our perception is not merely an array of elements just as an essay is not a sac of letters but a collection of words, sentences and paragraphs linked together. Objects are to our vision what chapters are to a book, stanzas to a poem. But how does our brain write its visual verses?
A clue comes from a region in parietal cortex at the top and back of our head, the intraparietal sulcus (IPS), involved in the construction of visual objects from their component features. The IPS is active when we attend to objects or maintain them in our visual short-term memory (VSTM). VSTM is the equivalent of a mental sketchpad and perhaps the seat of our visual imagination, allowing us to perceive while seeing naught. Since regions in the parietal cortex have been found to be organised in a retinotopic manner, the question I pose in my research is whether the structure of the visual maps found there relates to our imagination and reminiscence.
To investigate this, I use a VSTM task where participants are asked to remember several objects in different places in their visual field. However, instead of only looking at the activity while these stimuli are presented, I'm interested in whether the visual objects maintained in VSTM by the IPS are organised in a retinotopic way. If this is the case, the IPS could be the critical locus of our conscious, object-based perception.
But what's the point? Take for instance research into so-called "mind-reading", which allows us to decipher the content of our mental display by analysing the complex patterns of activity in the early visual cortex. However, this merely tells us what we know already - the image entering our eyes, not what objects we construct and thus attend to. Instead, knowing the detailed progression of objects built and dismantled tells us what we actually perceive. This is particularly important in the study of patients suffering "locked-in" syndrome, since we could allow them to effectively communicate with us by using their "inner eye". The chance to open these patients' door to the outside world is one of the true treasures that visual maps lead to...
These metaphoric maps stand for the various brain areas involved in vision. They are topographically structured, reflecting the organisation of the visual field on our eyes' retina, resulting in "retinotopic" maps drawn upon our brain's cortex. Each map is broken in half across our brain, with our left hemisphere processing information from our right field and vice versa. Furthermore, some of these half-maps are further broken into sections representing the upper and lower quadrants of our vision, such that we end up with four pieces adding up to each single map.
Researchers have charted numerous cortical maps, by using functional Magnetic Resonance Imaging (fMRI) to explore brain activation in response to stimulation of different parts of the visual field. Sixteen whole visual maps stretch from the Calcarine sulcus, in the Occipital lobe, at the back of our brain, to our prefrontal cortex, appearing grouped into different clusters, as islands aggregate into archipelagos. Our captain's question is inevitable: which one of them is real indeed?
In fact, they are all real, resulting in a cardinal problem for visual neuroscientists, understanding how perception depends on each of them: Does each serve a distinct goal and, so to speak, lead to a different bounty? And how is their content integrated into our seemingly unitary perception, into one vision?
Indeed, we know that some of the earlier maps contain information about the details in our visual world, breaking it up into edges, colour and motion. But our perception is not merely an array of elements just as an essay is not a sac of letters but a collection of words, sentences and paragraphs linked together. Objects are to our vision what chapters are to a book, stanzas to a poem. But how does our brain write its visual verses?
A clue comes from a region in parietal cortex at the top and back of our head, the intraparietal sulcus (IPS), involved in the construction of visual objects from their component features. The IPS is active when we attend to objects or maintain them in our visual short-term memory (VSTM). VSTM is the equivalent of a mental sketchpad and perhaps the seat of our visual imagination, allowing us to perceive while seeing naught. Since regions in the parietal cortex have been found to be organised in a retinotopic manner, the question I pose in my research is whether the structure of the visual maps found there relates to our imagination and reminiscence.
To investigate this, I use a VSTM task where participants are asked to remember several objects in different places in their visual field. However, instead of only looking at the activity while these stimuli are presented, I'm interested in whether the visual objects maintained in VSTM by the IPS are organised in a retinotopic way. If this is the case, the IPS could be the critical locus of our conscious, object-based perception.
But what's the point? Take for instance research into so-called "mind-reading", which allows us to decipher the content of our mental display by analysing the complex patterns of activity in the early visual cortex. However, this merely tells us what we know already - the image entering our eyes, not what objects we construct and thus attend to. Instead, knowing the detailed progression of objects built and dismantled tells us what we actually perceive. This is particularly important in the study of patients suffering "locked-in" syndrome, since we could allow them to effectively communicate with us by using their "inner eye". The chance to open these patients' door to the outside world is one of the true treasures that visual maps lead to...
