Constructive theories of brain function such as predictive coding posit that prior knowledge affects our experience of the world quickly and directly. However, it is yet unknown how swiftly prior knowledge impacts the neural processes giving rise to conscious experience. Here we used an experimental paradigm where prior knowledge augmented perception and measured the timing of this effect with magnetoencephalography (MEG). By correlating the perceptual benefits of prior knowledge with the MEG activity, we found that prior knowledge took effect in the time-window 80–95ms after stimulus onset, thus reflecting an early influence on conscious perception. The sources of this effect were localized to occipital and posterior parietal regions. These results are in line with the predictive coding framework.

Key words: predictive coding, contents of consciousness, meg, prior knowledge, conscious perception, cognitive penetrability

Abstract Multiunit activity was recorded in the optic tectum of awake pigeons with two electrodes at sites varying in depth and separated by 0.3 to 3.0 mm. Autocorrelation and cross-correlation functions were computed from the recorded spike trains to determine temporal relationships in the neuronal firing patterns. Cross-correlation analysis revealed that spatially separate groups of cells in the tectum show synchronous responses to a visual stimulus. Strong synchronization occurred in both superficial and deep layers of the tectum, in general with zero-phase shift. The response synchronization in the avian optic tectum resembles that observed in the mammalian cortex, suggesting that it may subserve common functions in visual processing.

Key words: Temporal coding, Synchronization, Oscillation, Optic tectum, Pigeon

Data are reviewed which suggest the following conclusions: 1) Neuronal activity is an important shaping factor in the self-organization of the developing nervous system. 2) Postnatal signals from sensory surfaces modulate neuronal activity and hence interfere with the self-organizing processes. 3) In the mammalian visual cortex these experience-dependent modifications are restricted to a critical period of postnatal development. 4) The rules which determine the direction of an activity-dependent change of neuronal connectivity resemble those postulated by Hebb for adaptive synaptic connections: Whether a connection is strengthened or weakened depends on the correlation between pre-and postsynaptic activity. 5) For a change to occur it is a prerequisite that the postsynaptic neuron is active. Hence, only sensory patterns capable of activating cortical neurons can induce modifications. 6) In addition to appropriate senory activity, internally generated permissive gating signals are necessary to permit experience-dependent modification. Thus, whether a change can occur in response to sensory stimulation does depend on the central state of the nervous system. 7) Stimulation conditions suitable for inducing long-term modifications are associated with an entry of Ca++-ions into intracellular compartments, suggesting the possibility that Ca++-ions serve as a trigger signal for the processes which cause long-term modifications of excitatory transmission. It is proposed that the experience-dependent modifications of neuronal interactions have an associative function and serve to assemble neurons according to functional criteria. The resulting selective interactions are thought to be the prerequisite for the development of cooperatively-coupled neuron assemblies.

Key words: visual cortex, receptive field, cortical cell, visual experience, striate cortex.

Consciousness has many different connotations, some of which are amenable to treatment within neurobiological description systems while others are not. It is possible to define in neurobiological terms the brain states associated with conscious-ness. It is also conceivable that neurobiology will ultimately provide a reductionistic explanation of mechanisms which enables the brain (1) to construct from the sparse and diverse signals of its sensors coherent models of its environment, including the or-ganism itself, and to generate abstract descriptions, (2) to iterate the same strategy to monitor its own states, thereby generating meta descriptions, (3) to weigh the combined results of these analyses in order to reach decisions and to generate adapted behavioural responses, and (4) to communicate through various channels at different levels of ab-straction the results of these cognitive processes to other brains. Since it became clear that the concept of the Cartesian theatre is untenable, that processes in the brain are highly distributed and that there is no single convergence center where the results of the numerous parallel operations are brought together for joint interpretation and decision making, analysis of processes that are in principle amenable to neurobiological explanation is in itself a major challenge. \\Problems of different nature are encountered if one attempts a reductionistic explanation of the subjective connotations of consciousness associated with self-awareness, attributes that are assessed by introspection and by extrapolation from one’s own awareness of mental states to that of others. I shall defend the position that these aspects of consciousness cannot be understood as emergent properties of individual brains alone but come into existence only through communication among brains whose cognitive abilities must be sufficiently developed to generate a theory of mind, i.e. to generate models of presumed states of the respective other brain. Thus, self-awareness and the ability to experience sensations as subjective reality would have to be considered as cultural achievements or, and this is equivalent, as the result of experiencing dialogues of the kind: “I know that you know that I know.” Hence, these aspects of consciousness come into existence only through a social learning process in which brains experience a class of mental phenom-ena that emerge only from mutual reflection. These phenomena are ontologically different from those qualified above as amenable to direct neurobiological investigation because unlike the latter they are the result of a dialogue among brains that got in-creasingly refined during cultural evolution. This is probably the reason why these phenomena appear as not deducible from analysis of individual brains in the same way as one can analyse the neuronal substrate of pattern recognition, memory or motor con-trol. My proposal is that the phenomena that give rise to the so called “hard problems” in the philosophy of consciousness, problems resulting from the ability to be aware of one’s own brain functions can be understood as emergent properties of brains without having to take a dualistic position; however, because these phenomena have a social or cultural origin and hence both a historical and interpersonal dimension, they cannot be understood as an emergent property of an isolated brain alone and hence transcend the reach of conventional neurobiological approaches.

Der Autor geht in seinem Beitrag der Frage nach, wie Wissen über die Welt in das menschliche Gehirn gelangt, wie es dort verankert wird und wie es bei der Wahrnehmung der Welt genutzt wird, um diese zu ordnen. Er betrachtet dabei sowohl die kognitiven Aspekte der Evolution und der Individualentwicklung als auch die neurobiologischen Grundlagen der Wahrnehmung im Hinblick auf die Frage nach der Repräsentation von Wahrnehmungsobjekten im Gehirn. Er zeigt anhand einer Abbildung, dass kognitive Systeme zunächst relativ elementare Kohärenzkriterien anwenden, um Bildelemente zusammenzufassen, die mit einer gewissen Wahrscheinlichkeit konstitutiv für Wahrnehmungsobjekte sind. In Bezug auf die Frage, wie nun das Wissen über diese in hohem Maße zweckmäßigen Kriterien ins Gehirn gelangt, um Ordnung in die Welt zu bringen, diskutiert der Autor verschiedene konkurrierende Hypothesen zur Struktur von Repräsentationen. Er untersucht ferner anhand von neurobiologischen Beispielen die Frage, auf welche Weise das in den Verbindungsarchitekturen der Großhirnrinde schlummernde Wissen aktiviert werden kann, um Wahrnehmungsprozesse zu strukturieren.

It is argued that perception is a highly constructive process and that the way in which we perceive the world and ourselves depends on a priori knowledge. Sources of this knowledge are evolution, early developmental imprinting and life long learning processes. Much of this knowledge is implicit and therefore there is no conscious recollection of the fact that perception is determined and constrained by priors that are genetically transmitted and acquired through early experience. Moreover, these priors are adapted to the mesoscopic scale of the world in which life has evolved and therefore cognitive abilities are to be seen as the result of evolutionary and developmental adaptations to an extremely narrow segment of the world as it is known to us to date. This has far reaching consequences for epistemic considerations and perhaps also for the management of cultural conflicts. If the perception of social conditions is also dependent on priors and if these priors are acquired early during development, they will exhibit culture specific traits but will remain implicit because episodic memory develops only several years after birth (childhood amnesia). In this case subjects cannot realize that their perception of social conditions depends on idiosyncratic, culture specific priors. What is perceived will be taken as absolute truth, acquire the status of convictions and cannot be altered by arguments.

Single unit activity was recorded from principal cells in the A-laminae of the cat dorsal lateral geniculate nucleus (dLGN). A steady state pattern of afferent activation was induced by presenting a continuously drifting square wave grating of constant spatial frequency to the eye (the dominant eye) that provided the excitatory input to the recorded cell. Intermittently, a second grating stimulus was presented to the other, nondominant, eye. In most neurones nondominant eye stimulation led to inhibition of relay cell responses. The latency of this suppressive effect was unusually long (up to 1 s) and its intensity and duration depended critically on the similarity between the gratings that were presented to the two eyes. Typically suppression was strongest when the gratings differed in orientation, direction of movement and contrast and when the nondominant eye stimulus was moving rather than stationary. Ablation of visual cortex abolished these long latency and feature-dependent interferences. We conclude that the visual cortex and the corticothalamic projections are involved in the mediation of these interocular interactions. We interpret our results as support for the hypothesis that corticothalamic feedback modifies thalamic transmission as a function of the congruency between ongoing cortical activation patterns and afferent retinal signals.