Biology subjects

Zeki, S.

Publications and source records attributed to Zeki, S..

9 recordsLinked to original sources

bioRxiv2023

Perceptual axioms are irreconcilable with Euclidean geometry

There are different definitions of axioms, but the one that seems to have general approval is that axioms are statements whose truths are universally accepted but cannot be proven; they are the foundation from which further propositional truths are derived. Previous attempts, led by David Hilbert, to show that all of mathematics can be built into an axiomatic system that is complete and consistent failed when Kurt Godel proved that there will always be statements which are known to be true but can never be proven within the same axiomatic system. But Godel and his followers took no account of brain mechanisms that generate and mediate logic. In this largely theoretical paper, but backed by previous experiments and our new ones reported below, we show that in the case of so-called "optical illusions" there exists a significant and irreconcilable difference between their visual perception and their description according to Euclidean geometry; when participants are asked to adjust, from an initial randomised state, the perceptual geometric axioms to conform to the Euclidean description, the two never match, although the degree of mismatch varies between individuals. These results provide evidence that perceptual axioms, or statements known to be perceptually true, cannot be described mathematically. Thus the logic of the visual perceptual system is irreconcilable with the cognitive (mathematical) system and cannot be updated even when knowledge of the difference between the two is available. Hence no one brain reality is more "objective" than any other.

neuroscience↗

bioRxiv2023

Neural patterns of conscious visual awareness in the Riddoch syndrome

The Riddoch syndrome is one in which patients blinded by lesions to their primary visual cortex can consciously perceive visual motion in their blind field, an ability that correlates with activity in motion area V5. Our assessment of the characteristics of this syndrome in patient ST, using multimodal MRI, showed that: 1. STs V5 is intact, receives direct subcortical input, and decodable neural patterns emerge in it only during the conscious perception of visual motion; 2. moving stimuli activate medial visual areas but, unless associated with decodable V5 activity, they remain unperceived; 3. STs high confidence ratings when discriminating motion at chance levels, is associated with inferior frontal gyrus activity. Finally, we report that STs Riddoch Syndrome results in hallucinatory motion with hippocampal activity as a correlate. Our results shed new light on perceptual experiences associated with this syndrome and on the neural determinants of conscious visual experience.

neuroscience↗

bioRxiv2022

The neural determinants of abstract beauty

We have enquired into the neural activity which correlates with the experience of beauty aroused by abstract paintings consisting of arbitrary assemblies of lines and colours. During the brain imaging experiments, subjects rated abstract paintings according to aesthetic appeal. There was low agreement on the aesthetic classification of these paintings among participants. Univariate analyses revealed higher activity with higher declared aesthetic appeal in both the visual areas and the medial frontal cortex. Additionally, representational similarity analysis (RSA) revealed that the experience of beauty correlated with decodable patterns of activity in visual areas. These results are broadly similar to those obtained in previous studies on facial beauty. With abstract art, it was the involvement of visual areas implicated in the processing of lines and colours while with faces it was of visual areas implicated in the processing of faces. Both categories of aesthetic experience correlated with increased activity in medial frontal cortex. We conclude that the sensory areas participate in the selection of stimuli according to aesthetic appeal and that it is the co-operative activity between the sensory areas and the medial frontal cortex that is the basis for the experience of abstract visual beauty. Further, this co-operation is enabled by "experience dependent" functional connections, in the sense that currently the existence and high specificity of these connections can only be demonstrated during certain experiences.

neuroscience↗

bioRxiv2021

The Neural Determinants of Beauty

What are the conditions that determine whether the medial orbito-frontal cortex (mOFC), in which activity correlates with the experience of beauty derived from different sources, becomes co-active with sensory areas of the brain during the experience of sensory beauty? We addressed this question by studying the neural determinants of facial beauty. The perception of faces correlates with activity in a number of brain areas, but only when a face is perceived as beautiful is the mOFC also engaged. The enquiry thus revolved around the question of whether a particular pattern of activity, within or between areas implicated in face perception, emerges when a face is perceived as beautiful, and which determines that there is, as a correlate, activity in mOFC. 17 subjects of both genders viewed and rated facial stimuli according to how beautiful they perceived them to be while the activity in their brains was imaged with functional magnetic resonance imaging. A univariate analysis revealed parametrically scaled activity within several areas in which the strength of activity correlated with the declared intensity of the aesthetic experience of faces; the list included the mOFC and two core areas strongly implicated in the perception of faces - the occipital face area (OFA), fusiform face area (FFA)- and, additionally, the cuneus. Multivariate analyses showed strong patterns of activation in the FFA and the cuneus and weaker patterns in the OFA and the pSTS. It is only when specific patterns emerged in these areas that there was co-activation of the mOFC, in which a strong pattern also emerged during the experience of facial beauty. A psychophysiological interaction analysis with mOFC as the seed area revealed the involvement of the right FFA and the right OFA. We conjecture that these collective patterns of activity constitute the neural basis for the experience of facial beauty, bringing us a step closer to understanding the neural determinants of aesthetic experience.

neuroscience↗

bioRxiv2018

The Biological Basis of the Experience of Constant Colour Categories

In the work reported here, we used the Land Colour Mondrian experiments to test the degree to which subjects vary in their perception of colour categories. Twenty subjects of different ethnic and cultural backgrounds, for all but one of whom English was not the primary language, viewed 8 patches of different colour in two Mondrian displays; each patch, when viewed, was made to reflect identical ratios of long-, middle- and short-wave light. Subjects were asked to match the colour of the viewed patch with that of the Munsell chip coming closest in colour to that of the viewed patch, without using language. Overall, there was no variability in categorizing colours as red, yellow, brown and green but a small variability in categorizing them as purple, blue, orange and turquoise. In terms of hue, we found significantly less variability in matching warm hues than in cool ones. We interpret the lack of significant variability between subjects in the matches made as a pointer to similar computational mechanisms being employed in different subjects to perceive colours, thus permitting subjects to assume that their categorization of colours has universal agreement and assent.

neuroscience↗

bioRxiv2018

The Biological Basis of Mathematical Beauty

Through our past studies of the neurobiology of beauty, we have come to divide aesthetic experiences into two broad categories: biological and artifactual. The aesthetic experience of biological beauty is dictated by inherited brain concepts, which are resistant to change even in spite of extensive experience. The experience of artifactual beauty on the other hand is determined by post-natally acquired concepts, which are modifiable throughout life by exposure to different experiences (Zeki, 2009). Hence, in terms of aesthetic rating, biological beauty (in which we include the experience of beautiful faces or human bodies) is characterized by less variability between individuals belonging to different ethnic origins and cultural backgrounds or the same individual at different times. Artifactual beauty (in which we include the aesthetic experience of human artifacts such as buildings and cars) is characterized by greater variability between individuals belonging to different ethnic and cultural groupings and by the same individual at different times. In this paper, we present results to show that the experience of mathematical beauty (Zeki et al 2014), even though it constitutes an extreme example of beauty that is dependent upon (mathematical) culture and learning, belongs to the biological category and obeys one of its characteristics, namely a lesser variability in terms of the aesthetic ratings given to mathematical formulae experienced as beautiful.

neuroscience↗

bioRxiv2017

Very Early Responses to Colour Stimuli Detected in Prestriate Visual Cortex by Magnetoencephalography (MEG)

Previous studies with the visual motion and form systems show that visual stimuli belonging to these categories trigger much earlier latency responses from the visual cortex than previously supposed and that the source of the earliest signals can be located in either the prestriate cortex or in both the striate (V1) and prestriate cortex. This is consistent with the known anatomical connections since, in addition to the classical retino-geniculo-striate cortex input, there are direct anatomical inputs from both the lateral geniculate nucleus and the pulvinar that reach the prestriate visual cortex without passing through V1. In pursuing our studies, we thought it especially interesting to study another cardinal visual attribute, namely colour, to learn whether colour stimuli also provoke very early responses, at less than 50 ms, from visual cortex. To address the question, we asked participants to view stimuli that changed in colour and used magneto-encephalography to detect very early responses (< 50 ms) in the occipital visual cortex. Our results show that coloured stimuli also provoke an early cortical response (M30), with an average peak time at 30.8 ms, thus bringing the colour system into line with the visual motion and form systems. We conclude that colour signals reach visual cortex, including prestriate visual cortex, earlier than previously supposed.\n\nKey points summaryO_LIWe measured visual evoked responses to colour stimuli using magnetoencephalography.\nC_LIO_LIAn early response was identified, at around 30 ms after stimulation.\nC_LIO_LIThe sources of the response were estimated to be in prestriate cortex.\nC_LIO_LIColour signals thus appear to evoke very early cortical responses, just like form and motion signals.\nC_LI\n\nAbbreviations list

neuroscience↗

bioRxiv2016

The Constancy of Colored After-Images

We undertook psychophysical experiments to determine whether the color of the after-image produced by viewing a colored patch which is part of a complex multi-colored scene depends on the wavelength-energy composition of the light reflected from that patch. Our results show that, just as the color of a patch which is part of a complex scene is independent of the wavelength-energy composition of the light coming from it alone, but depends as well on the wavelength-energy composition of the light coming from its surrounds, so is the color of its after-image. Hence, traditional accounts of after-images as being the result of retinal adaptation or the perceptual result of physiological opponency, are inadequate. We propose instead that the color of after-images is generated after colors themselves are generated in the visual brain.

neuroscience↗

bioRxiv2016

The Bayesian-Laplacian Brain

We outline what we believe could be an improvement in future discussions of the brain acting as a Bayesian-Laplacian system. We do so by distinguishing between two broad classes of priors on which the brains inferential systems operate: in one category are biological priors ({beta} priors) and in the other artifactual ones ( priors). We argue that {beta} priors, of which colour categories and faces are good examples, are inherited or acquired very rapidly after birth, are highly or relatively resistant to change through experience, and are common to all humans. The consequence is that the probability of posteriors generated from {beta} priors having universal assent and agreement is high. By contrast, priors, of which man-made objects are examples, are acquired post-natally and modified at various stages throughout post-natal life; they are much more accommodating of, and hospitable to, new experiences. Consequently, posteriors generated from them are less likely to find universal assent. Taken together, in addition to the more limited capacity of experiment and experience to alter the {beta} priors compared to priors, another cardinal distinction between the two is that the probability of posteriors generated from {beta} priors having universal agreement is greater than that for priors. The two categories are not, however, always totally distinct and can merge into one another to varying extents, resulting in posteriors that draw upon both categories.

neuroscience↗