We suggested recently that attention can be understood as inferring the level of uncertainty or precision during hierarchical perception. In this paper, we try to substantiate this claim using neuronal simulations of directed spatial attention and biased competition. These simulations assume that neuronal activity encodes a probabilistic representation of the world that optimizes free-energy in a Bayesian fashion. Because free-energy bounds surprise or the (negative) log-evidence for internal models of the world, this optimization can be regarded as evidence accumulation or (generalized) predictive coding. Crucially, both predictions about the state of the world generating sensory data and the precision of those data have to be optimized. Here, we show that if the precision depends on the states, one can explain many aspects of attention. We illustrate this in the context of the Posner paradigm, using the simulations to generate both psychophysical and electrophysiological responses. These simulated responses are consistent with attentional bias or gating, competition for attentional resources, attentional capture and associated speed-accuracy trade-offs. Furthermore, if we present both attended and non-attended stimuli simultaneously, biased competition for neuronal representation emerges as a principled and straightforward property of Bayes-optimal perception.

/pdf/attention-uncertainty-and-free-energy-1n4sc6fr33.pdf

Attention, Uncertainty, and Free-Energy

(Ada­ mlik 1870). But it has only recently been possible to study the relation of single cell activity within this structure to both movement and vision. This cellular approach, along with new anatomical, physiological, and behavioral methods, has enabled the investigation of the machinery whereby the visual stimulus initiates motor movement. It is these advances that we concentrate on in this review. We emphasize the primate superior colliculus because most of the work relating to movement has been done in the rhesus monkey, Macaca mulatta. At the same time we draw on work done on the cat and tree shrew to supplement areas as yet unexplored in the monkey, although many interesting facets of work on these and other species are not considered. Other recent reviews have considered many of these other aspects (Sprague et al 1970, Gordon 1975, Sprague 1972,

Visual-Motor Function of the Primate Superior Colliculus

Afferent signals that guide orienting movements converge in the deeper layers of the SC in a wide variety of animals. The sensory cells are arranged topographically according to their receptive-field locations and, thereby, form maps of sensory space. Maps of visual, somatosensory, and/or auditory space have been obtained in the iguana, mouse, hamster, barn owl, chinchilla, cat, and monkey. The deeper layers of the SC also contain neurons involved in the generation of movements of the eyes, head, vibrissae, and pinnae. Thus the SC, a site containing multiple sensory maps and perhaps multiple motor maps, has been selected by many investigators as a structure for investigating the problem of sensorimotor integration. In the mammalian nervous system, emphasized in this review, much remains to be learned about the structure, organization, and function of the SC. While anatomical studies continue to add to the knowledge of the sources of afferent projections, their pattern of laminar termination, and the source and destination of efferent projections, relatively little is known about the intrinsic organization of the colliculus, especially the deeper layers. Recently, electrophysiological studies have moved from an emphasis on the sensory and motor properties of collicular neurons to an examination of the maps of auditory and somatosensory space and the correspondence of these maps. In the future, major efforts aimed at identifying the functional properties of cells that project to the SC from diverse brain regions as well as the functional properties that project to the various structures receiving input from the colliculus are needed. A combination of anatomical and electrophysiological methods is required to describe the signal transforms that occur between the SC and motor areas (such as the paramedian pontine reticular formation) closer to the final common pathway. Conceptual and empirical work is needed to develop and test models of how the dynamic visual and auditory maps found in the primate SC are generated. In general, new and/or improved models of the role of the SC in sensorimotor integration are needed as guides for future research. A point of view emphasized here is that it may be fruitful to examine the function of the SC from a motor perspective. The nature of the motor command imposes constraints on the configuration of signals that can initiate movements and thereby determines the required transformation of sensory signals.

Translation of sensory signals into commands for control of saccadic eye movements: role of primate superior colliculus

Méthodes : Sur une série de 31 femmes présentant des varices périnéales d’origine extrasaphéniennes ayant bénéficié d’une exploration radiologique veineuse pelvienne et de l’embolisation des veines incontinentes nous avons étudié les résultats et les corrélations anatomo-clinique entre les varices et les signes cliniques de l’insuffisance veineuse pelvienne. Un sous-groupe B de 23 patientes présentant une insuffisance veineuse pelvienne et des signes cliniques a été comparé à un groupe A de 4 patientes qui ne présentaient pas d’insuffisance veineuse pelvienne à l’exploration. Nous avons choisi d’étudier 3 signes cliniques : la douleur pelvienne et la douleur des membres inférieurs survenant au début ou pendant les règles ainsi que la dyspareunie. La symptomatologie a été évaluée sur une échelle analogique de 0 à 10 et un score clinique (de 0 à 30) a été établi en ajoutant ces 3 chiffres.

http://link.springer.com/content/pdf/10.1007/BF02973687.pdf

Références bibliographiques: La fibroscopie bronchique

To execute voluntary movements, the central nervous system must transform the neural representation of the direction, amplitude, and velocity of the limb, represented by the activity of cortical and subcortical neurons, into signals that activate the muscles that move the limb. This task is equivalent to solving an "ill-posed" computational problem because the number of degrees of freedom of the musculoskeletal apparatus is much larger than that specified in the plan of action. Some of the mechanisms and circuitry underlying the transformation of motor plans into motor commands are described. A central feature of this transformation is a coarse map of limb postures in the premotor areas of the spinal cord. Vectorial combination of motor outputs among different areas of the spinal map may produce a large repertoire of motor behaviors.

https://science.sciencemag.org/content/sci/253/5017/287.full.pdf

Computations underlying the execution of movement: a biological perspective

The activity of neck muscles was recorded in the alert, head-fixed cat together with the horizontal and vertical components of eye movements. Electromyographic activity of obliquus capitis cranialis and caudalis, and longissimus capitis, is closely related to horizontal eye position in the orbit both during spontaneous eye movements and vestibular nystagmus. The activity of splenius also shows this relationship but the coupling is less tight, probably because of the postural function of this muscle.

Horizontal Eye Position-related Activity in Neck Muscles of the Alert Cat

Development of fixation and pursuit eye movements in human infants.

The electromyographic (EMG) activity of different neck muscles in relation to gaze orientation has been studied in alert trained cats When the head is kept fixed, the activity of these muscles is proportional to eye eccentricity in the horizontal as well as in the vertical planes On basis of this tonic activity, a preferential orientation can be attributed to each muscle: upward and lateral for biventer, rectus and complexus, and downward and lateral for longissimus, splenius and obliquus capitis cranialis Fluctuations in this modulation of the EMG activity by eye position can be observed When the head is free to move, the muscles show phasic discharges having similar preferential orientations For a given muscle, this orientation covers a quite large angle: many muscles contribute to a given movement The timing of the discharge of the different muscles as a function of the direction of the head movement was examined It was found that the latency, ie the delay between the discharge and movement onset, progressively increases as the movement direction diverges from the preferential orientation of the muscle It has been noted that the muscles having an upward preferential orientation may show, in relation to downward movements, inhibition occurring prior to the onset of the head movement The same muscles may also increase their activity around the midcourse of downward movements Thus, the head motor system controls the direction and amplitude parameters not only by selectively activating the appropriate muscles but also by sequencing their activity in a subtle way to start, control the trajectory and stop the movement, reminiscent of what has been described for limb movements

Neck muscle activity in eye--head coordinated movements.

In foveate as well as in afoveate species, most displacements of the line of sight are accomplished by combined eye and head rotations. This has been demonstrated in a number of studies, among others by Bartz (1966) in man, Bizzi et al (1971) in the monkey, Gresty (1975) in the guinea-pig and Collewijn (1977) in the rabbit. Moreover, it has been shown that neck muscles are activitated in synchrony with eye saccades (Bizzi et al, 1972; Guitton et al, 1980). The torque exerted by the neck also increases together with eye saccades directed towards the ipsilateral side (Fuller, 1981). During vestibular stimulation in cats elicited by passive head rotation, Ezure and Sasaki (1978) have shown that a similar vestibular signal reached neck and eye muscles. Fuller (1981), in the rabbit, evidenced a close linkage between head torque and vestibular quick phases. Gresty (1975) had previously shown a similar phenomenon in the guinea-pig. Outerbridge and Melville-Jones (1971) in man also mentioned the same synchronization.

The Relation of Neck Muscles Activity to Horizontal Eye Position in the Alert Cat. II: Head Free

Eye position-related activity in deep neck muscles of the alert cat.

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