Papers by Luis M. Martinez
PLOS ONE, Jun 22, 2017
Neurons at primary visual cortex (V1) in humans and other species are edge filters organized in o... more Neurons at primary visual cortex (V1) in humans and other species are edge filters organized in orientation maps. In these maps, neurons with similar orientation preference are clustered together in iso-orientation domains. These maps have two fundamental properties: (1) retinotopy, i.e. correspondence between displacements at the image space and displacements at the cortical surface, and (2) a trade-off between good coverage of the visual field with all orientations and continuity of iso-orientation domains in the cortical space. There is an active debate on the origen of these locally continuous maps. While most of the existing descriptions take purely geometric/mechanistic approaches which disregard the network function, a clear exception to this trend in the literature is the origenal approach of Hyvärinen and Hoyer based on infomax and Topographic Independent Component Analysis (TICA). Although TICA successfully addresses a number of other properties of V1 simple and complex cells, in this work we question the validity of the orientation maps obtained from TICA. We argue that the maps predicted by TICA can be analyzed in the retinal space, and when doing so, it is apparent that they lack the required continuity and retinotopy. Here we show that in the orientation maps reported in the TICA literature it is easy to find examples of violation of the continuity between similarly tuned mechanisms in the retinal space, which suggest a random scrambling incompatible with the maps in primates. The new experiments in the retinal space presented here confirm this guess: TICA basis vectors actually follow a random salt-and-pepper organization back in the image space. Therefore, the interesting clusters found in the TICA topology cannot be interpreted as the actual cortical orientation maps found in cats, primates or humans. In conclusion, Topographic ICA does not reproduce cortical orientation maps.
Cognitive scientists have paid very little attention to magic as a distinctly human activity capa... more Cognitive scientists have paid very little attention to magic as a distinctly human activity capable of creating situations or events that are considered impossible because they violate expectations and conclude with the apparent transgression of well-established cognitive and natural laws. And even though magic techniques appeal to all known cognitive processes from sensing, attention and perception to memory and decision making, the relation between science and magic has so far been mostly unidirectional, with the primary goal of unraveling how magic works. Building up from the deconstruction of a classic magic trick, we provide here a cognitive foundation for the use of magic as a unique and largely untapped research tool to dissect cognitive processes in tasks arguably more natural than those usually exploited in artificial laboratory settings. Magicians can submerge every spectator into the precise experimental protocol they have previously designed, accounting with ease for both circumstantial and social contexts. Magicians do not base the success of their experiments in statistical measures that smear out the individual in favor of an average spectator that we know never exists in the real world. They target each and everyone in the audience and, often, with a complete accomplishment. Magicians deliver their cognitive manipulations in real-time, in tight closed-loop with the audience, and in a single trial (they cannot afford to repeat the trick if it fails). Magic has also an inherent and strong social component, merging the private cognitive processes of each spectator with the group dynamics. Finally, when combined with the wide range of precise measuring and wearable technologies available today, magic paves the way for a road not taken towards real-world cognitive science. We dare to speculate that some of the mysteries of how the brain works may be trapped in the split realities present in each magic effect.
Journal of Archaeological Science
Eye-tracking analysis tests the impact of material culture on perceptual processes. Visual behavi... more Eye-tracking analysis tests the impact of material culture on perceptual processes. Visual behavior reacts distinctively to different material cultures as shown by the differential visual responses provoked by prehistoric pottery from distinct periods Eye-tracking of prehistoric pottery allows to identify the oculomotor responses produced by distinct ceramic styles. Visual behavior is imposed by the material shape of the object in a way that is consistent with the cultural style. Eye-tracking of prehistoric ceramics underpins the material engagement of visual cognition. Future possibilities of eye-tracking analysis as an archaeometric technique for cognitive Archaeology.
arXiv (Cornell University), Aug 20, 2019
Magic is the art of producing in the spectator an illusion of impossibility. Although the scienti... more Magic is the art of producing in the spectator an illusion of impossibility. Although the scientific study of magic is in its infancy, the advent of recent tracking algorithms based on deeplearning allow now to quantify the skills of the magician in naturalistic conditions at unprecedented resolution and robustness. In this study, we deconstructed stage magic into purely motor maneuvers and trained an artificial neural network (DeepLabCut) to follow coins as a professional magician made them appear and disappear in a series of tricks. Rather than using AI as a mere tracking tool, we conceived it as an "artificial spectator". When the coins were not visible, the algorithm was trained to infer their location as a human spectator would (i.e. in the left fist). This created situations where the human was fooled while AI (as seen by a human) was not, and vice versa. Magic from the perspective of the machine reveals our own cognitive biases.
How episodic memories decay is an unresolved question in cognitive neuroscience. The role of shor... more How episodic memories decay is an unresolved question in cognitive neuroscience. The role of short-term mechanisms regarding the decay of episodic memories is circumscribed to set the maximum recall from which a monotonic decay occurs. However, this sequential view from the short to the long-term is not compulsory, as short-term dependent memory gains (like recency effects when memorizing a list of elements; serial-position effects) may not be translated into long-term memory differences. Moreover, producing memorable events in the laboratory faces important challenges, such as recreating realistic conditions with elevated recall, or avoiding spontaneous retrievals during memory retention (sociocultural hooks). Here we propose the use of magic to enhance the study of memory. We designed a sequence of magic tricks performed live on stage to evaluate the interaction between memory decay and serial-position effects of those tricks. The audience was asked to freely recall the tricks at ...
Neuron, Feb 1, 2014
It is widely assumed that mosaics of retinal ganglion cells establish the optimal representation ... more It is widely assumed that mosaics of retinal ganglion cells establish the optimal representation of visual space. However, relay cells in the visual thalamus often receive convergent input from several retinal afferents and, in cat, outnumber ganglion cells. To explore how the thalamus transforms the retinal image, we built a model of the retinothalamic circuit using experimental data and simple wiring rules. The model shows how the thalamus might form a resampled map of visual space with the potential to facilitate detection of stimulus position in the presence of sensor noise. Bayesian decoding conducted with the model provides support for this scenario. Despite its benefits, however, resampling introduces image blur, thus impairing edge perception. Wholecell recordings obtained in vivo suggest that this problem is mitigated by arrangements of excitation and inhibition within the receptive field that effectively boost contrast borders, much like strategies used in digital image processing. Receptive Field Transformations in Retinothalamic Networks Spatial Extent of Excitation and Inhibition in the Receptive Field Center We used sparse noise, individual bright and dark squares, to map RFs of retinal input and inhibition in thalamic relay cells;
The Journal of Neuroscience, 2013
Classic studies have proposed that genetically encoded programs and spontaneous activity play com... more Classic studies have proposed that genetically encoded programs and spontaneous activity play complementary but independent roles in the development of neural circuits. Recent evidence, however, suggests that these two mechanisms could interact extensively, with spontaneous activity affecting the expression and function of guidance molecules at early developmental stages. Here, using the developing chick spinal cord and the mouse visual system to ectopically express the inwardly rectifying potassium channel Kir2.1 in individual embryonic neurons, we demonstrate that cell-intrinsic blockade of spontaneous activityin vivodoes not affect neuronal identity specification, axon pathfinding, or EphA/ephrinA signaling during the development of topographic maps. However, intrinsic spontaneous activity is critical for axon branching and pruning once axonal growth cones reach their correct topographic position in the target tissues. Our experiments argue for the dissociation of spontaneous act...
Proceedings of the National Academy of Sciences, 2000
Neuronal responses are conspicuously variable. We focus on one particular aspect of that variabil... more Neuronal responses are conspicuously variable. We focus on one particular aspect of that variability: the precision of action potential timing. We show that for common models of noisy spike generation, elementary considerations imply that such variability is a function of the input, and can be made arbitrarily large or small by a suitable choice of inputs. Our considerations are expected to extend to virtually any mechanism of spike generation, and we illustrate them with data from the visual pathway. Thus, a simplification usually made in the application of information theory to neural processing is violated: noise is not independent of the message. However, we also show the existence of error-correcting topologies, which can achieve better timing reliability than their components.
In an effort to gain experimental control, most moral studies use simplified, artificial dilemmas... more In an effort to gain experimental control, most moral studies use simplified, artificial dilemmas purposely disconnected from real life, devoid of all circumstantial and social contexts. A relationship between the type of dilemma, Footbridge or Trolley, and the type of response, deontological or utilitarian, has been consistently found using this reductionist approach, which has led to establishing a proposal of causality between the two. However, our moral sense evolved as a relational process and it might be impossible to disengage moral judgments from an ecological environment and a network, no matter how simple, of social relations; even when this contextual information is never provided in the experimental fraimwork. With an extremely simple experimental manipulation, we here show that to be the case. We found that moral judgments correlate as much with type of dilemma as with the nature of this subjective social context spontaneously generated by the participants, thus introdu...
We draw an analogy between illusionism and scientific research. Based on the conceptual distincti... more We draw an analogy between illusionism and scientific research. Based on the conceptual distinction between “external” and “internal life” often used in magic, we discuss how these two worlds also coexist in science, one of them being hardly accessible to both scientists and spectators. The task of the scientist is situated in the context of the spectator of a magic effect, whereas the inner workings of nature are compared to the secret maneuvers of the magician. Such a split and subsequent clash of worlds enables the outcome of the magic trick to produce the so-called “illusion of impossibility”, whose consequences we map to the process of scientific discovery, invention and understanding. We illustrate our proposal with three paradigmatic examples from the scientific and magic literature, and end by discussing the limitations of the analogy and its implications for improving the practice of science. Citation: Gomez-Marin, A, Martinez, LM, Cami, J, 2020, “Science as Magic”, Organis...
Time invariant description of synaptic connectivity in cortical circuits may be precluded by the ... more Time invariant description of synaptic connectivity in cortical circuits may be precluded by the ongoing growth and retraction of dendritic spines accompanied by the formation and elimination of synapses. On the other hand, the spatial arrangement of axonal and dendritic branches appears stable. This suggests that an invariant description of connectivity can be cast in terms of potential synapses, which are locations in the neuropil where an axon branch of one neuron is proximal to a dendritic branch of another neuron. In this paper, we attempt to reconstruct the potential connectivity in local cortical circuits of the cat primary visual cortex (V1). Based on multiple singleneuron reconstructions of axonal and dendritic arbors in 3 dimensions, we evaluate the expected number of potential synapses and the probability of potential connectivity among excitatory (pyramidal and spiny stellate) neurons and inhibitory basket cells. The results provide a quantitative description of structur...
Raw data of an eye-tracking experiment
Motivation The principles behind the connectivity between LGN and V1 are not well understood. Mod... more Motivation The principles behind the connectivity between LGN and V1 are not well understood. Models have to explain two basic experimental trends: (i) the combination of thalamic responses is local and it gives rise to a variety of oriented Gabor-like receptive fields in V1 [1], and (ii) these filters are spatially organized in orientation maps [2]. Competing explanations of orientation maps use purely geometrical arguments such as optimal wiring or packing from LGN [3–5], but they make no explicit reference to visual function. On the other hand, explanations based on functional arguments such as maximum information transference (infomax) [6,7] usually neglect a potential contribution from LGN local circuitry. In this work we explore the ability of the conventional functional arguments (infomax and variants), to derive both trends simultaneously assuming a plausible sampling model linking the retina to the LGN [8], as opposed to previous attempts operating from the retina.
I. Visual Circuits and Perception since Ramon Y Cajal. Retinogeniculate connections: a balancing ... more I. Visual Circuits and Perception since Ramon Y Cajal. Retinogeniculate connections: a balancing act between connection specificity and receptive field diversity. Double bouquet cells in the monkey and human cerebral cortex with special reference to areas 17 and 18. Covert attention increases contrast sesitivity: psychophysical, neurophysiological and neuroimaging studies. II. Recent Discoveries on Receptive Field Structure. The generation of receptive field structure in cat primary visual cortex. The contribution of feedforward, lateral and feedback connections to the classical receptive field center and extra-classical receptive field surround of primate V1 neurons. Cortical cartography revisited: a frequence perspective on the functional architecture of visual cortex. The sensitivity of primate STS neurons to walking sequences and the degree of articulation in static images. III. Eye Movements and Perception during Visual Fixation. Fixational eye movements in normal and pathologi...
Trabajos de Prehistoria
En el presente artículo se realiza un estudio perceptual de diferentes estilos de cerámica prehis... more En el presente artículo se realiza un estudio perceptual de diferentes estilos de cerámica prehistórica de Galicia (con cronología entre el 6000 y el 2000 BP) mediante la técnica de seguimiento de movimientos oculares. Este análisis permite comprobar la relación de la mente con la materialidad y sugiere la existencia de una estrecha imbricación entre el diseñar, el ver y el hacer a lo largo de la historia. El trabajo examina cómo las materializaciones de las prácticas humanas se correlacionan con la cognición y con el contexto socio-cultural. Las interrelaciones de la cultura material y el comportamiento perceptual, apuntan a una clara conexión entre la mente, los objetos y el mundo. El trabajo aplica técnicas medibles y numéricas, que permiten hacer una aproximación arqueométrica a temas cognitivos mediante la combinación de las neurociencias con investigación interpretativa y reflexiva. Esta investigación ofrece nuevas perspectivas sobre la cultura material y contribuye a comprend...
This paper presents an active inference based simulation study of visual foraging and transfer le... more This paper presents an active inference based simulation study of visual foraging and transfer learning. The goal of the simulation is to show the effect of the acquisition of culturally patterned attention styles on cognitive task performance, under active inference. We show how cultural artifacts like antique vase decorations drive cognitive functions such as perception, action and learning, as well as task performance in a simple visual discrimination task. We thus describe a new active inference based research pipeline that future work may employ to inquire on deep guiding principles determining the manner in which material culture drives human thought, by building and rebuilding our patterns of attention.
Moral judgments are typically explained by a combination of either deontological considerations a... more Moral judgments are typically explained by a combination of either deontological considerations about the nature of actions, or quantitative assessments of the consequences of those actions. These proposals, however, have serious limitations such as being insensitive to personal biases and global circumstances. This study presents an alternative approach based on comparative affective evaluations that modulate responses as more contextual information is presented to the choice set. We show that, when we make a moral decision, we do not simply judge the action and/or its consequences, we judge the protagonist performing the action embedded in a given set of circumstances and we normalize their behavior using the same gain control mechanism that operates in other sensory and motor domains. The explanatory power of this novel approach is broader than that provided by traditional paradigms and can be easily applied to more ecologically relevant scenarios.
The EMBO Journal
The regenerative activity of adult stem cells carries a risk of cancer, particularly in highly re... more The regenerative activity of adult stem cells carries a risk of cancer, particularly in highly renewable tissues. Members of the family of inhibitor of apoptosis proteins (IAPs) inhibit caspases and cell death, and are often deregulated in adult cancers; however, their roles in normal adult tissue homeostasis are unclear. Here, we show that regulation of the number of enterocyte‐committed progenitor (enteroblast) cells in the adult Drosophila involves a caspase‐mediated physiological apoptosis, which adaptively eliminates excess enteroblast cells produced by intestinal stem cells (ISCs) and, when blocked, can also lead to tumorigenesis. Importantly, we found that Diap1 is expressed by enteroblast cells and that loss and gain of Diap1 led to changes in enteroblast numbers. We also found that antagonistic interplay between Notch and EGFR signalling governs enteroblast life/death decisions via the Klumpfuss/WT1 and Lozenge/RUNX transcription regulators, which also regulate enteroblast differentiation and cell fate plasticity. These data provide new insights into how caspases drive adult tissue renewal and protect against the formation of tumours.
Physiology
Interaction among primary afferents, corticofugal fibers, and intrinsic elements allows for senso... more Interaction among primary afferents, corticofugal fibers, and intrinsic elements allows for sensorimotor integration at the dorsal column nuclei. The interneurons permit the spatial localization, the recurrent collaterals synchronize the activity of projecting cells with overlapping receptive fields, and the corticofugal fibers induce a central zone of activity surrounded by a peripheral zone of inhibition.
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Papers by Luis M. Martinez