Is selection a subjective process
Human perception is limited by its sense organs, whereby the processing of information in the brain means that human perception's claim to objectivity is always questionable. In order to achieve the goal of gaining information about the environment, to behave successfully in its environment and not to be overwhelmed by the multitude of information, the brain uses the means of selection or filtering, d. In other words, perception is a selection and organization process or, ultimately, an active construction process. Although all people have the same sensory organs and the absorption of stimuli is almost the same for all people, perception is subject to subjective interpretations that also decide what they perceive, how they interpret it, what importance they attach to what they perceive and what reaction they respond to demonstrate. What people perceive is also to a large extent contextual, because the human brain always tries to adapt to the environment and its challenges.
The processing and evaluation of stimuli depends on numerous external and internal factors and is therefore subjective, i.e. every person perceives their environment in their own specific, individual way. This applies in particular to the area of social perception, where distortions of perception, different interpretations and personal evaluations can lead to considerable misunderstandings. How people perceive their living conditions, their fellow human beings and their environment has a decisive influence on their self-image, their well-being, their communication behavior, their interpersonal relationships and their success, whereby these factors in turn influence current and future perception patterns.
Critical state of the networks as a possible selection mechanism of subjective perception
Rustling leaves, light rain on the window, a quietly ticking clock, dull noises, just above the hearing threshold, are perceived once in one moment and not in the next, even if you or the tones have not changed. Studies have shown that an incoming stimulus, such as a sound, an image or a touch, is processed differently in each case, even if the stimulus is exactly the same. This is because the extent to which a stimulus activates the relevant brain regions depends on the current state of the networks to which these regions belong. However, it is unclear what influences this constantly fluctuating state of the networks and whether this occurs randomly or follows a rhythm. Stephani et al. (2020) have now found out how this processing works, with a critical condition playing a decisive role in this. These relationships were investigated using thousands of small, consecutive electrical currents that were applied to the forearm of the participants in order to stimulate the main nerve in the arm. These stimulations in turn led to an initial reaction 20 milliseconds later in the somatosensory cortex, and the EEG pattern shows how easily each individual stimulus excites the brain. The brain reacts more strongly to a stimulus, the stronger the networks can be stimulated at the moment in which the stimulus information enters the cortex. Depending on the condition, the nerve cells in the primary somatosensory cortex are easier or more difficult to excite, whereby the excitability determines how the stimulus is processed further, i.e. In other words, it already influences how the brain deals with a stimulus at the entrance to the cerebral cortex and not only at higher, downstream levels.
There is always a certain amount of activity between the neurons of a network, even if no external influences appear to be acting on it, i. In other words, the system is never completely inactive. Rather, they constantly receive information, for example from inside the body, because they watch over the heartbeat, digestion or breathing, over the position in space and internally generated thoughts. The neurons are active even when they are isolated from any input, so that these internal processes constantly influence the excitability or readiness of various brain networks. Their dynamic ultimately determines the excitability of the system and thus also the reaction to a stimulus. However, it is not left to chance how strongly the cortex is excitable, because the change between lesser and greater irritability follows a certain temporal pattern, whereby the current state depends on the previous one and in turn influences the subsequent one. One speaks here of a long-term time dependency or a long-lasting autocorrelation. The fact that the cortex varies in its excitability suggests that its networks are close to a so-called critical state, i.e. that is, they always fluctuate in a delicate balance between excitement and inhibition. This critical state may be decisive for brain function, because it allows as much information as possible to be transmitted and processed, so that this balance could also determine how the brain processes sensory influences. It is believed to serve as an adaptation mechanism to cope with the variety of information that is constantly coming in from the environment; That is, a single stimulus should neither excite the entire system at once nor go away too quickly.
However, it is still unclear what this means for subjective perception, because other processes will probably also play a role here, such as attention. If you direct this to something else, the incoming, less noticed stimulus can still cause an initial, strong brain reaction, but higher downstream processes in the cerebrum could then prevent it from being consciously perceived.
Alpha waves as a correlate of perceptual distortions
As is well known, the human brain systematically generates more or less distorted perceptions of the world so that people develop their own subjective reality, whereby this cognitive distortion is usually an unconscious phenomenon. But people can overcome such a personal bias under certain conditions. Using an assessment task with a chronological order, Grabot & Kayser (2020) checked whether Alpha waves related to such distortions of perception in the brain. It was found in the EEG data that weaker alpha waves meant that subjects resisted an experimentally induced bias, while stronger alpha waves showed up when subjects decided according to their personal inclination. The spontaneous alpha wave activity therefore seems to be a specific indicator of cognitive distortions, even before the actual decision is made.
An essential basic principle of subjective perception is also that missing information in the brain to be completedwhere this completed perception often appears more trustworthy than reality. Although we know very well that the perception often does not correspond to an objective reality, von Ehinger et al. (2017) have shown experimentally that this fact is not only accepted subconsciously, but that this subjective perception is even preferred compared to reliable information. In order to cope with everyday life, people have to constantly assess and weight several sensory impressions according to their reliability, because when crossing a street, for example, one prefers to rely on the sense of sight. On the other hand, on a foggy day with limited visibility, one would pay more attention to traffic noise, i.e. classify the acoustic information as more reliable. Also completed in the case of the Blind spot the brain automatically retrieves the missing information by accessing the content of the neighboring areas so that people do not even notice this gap, unless a specific template is used for this purpose. This completion by the brain is called filling-in effect and is completely sufficient in everyday life. In a study, test subjects were asked to compare two circles (seamlessly or continuously striped) and select the circle that was continuously striped. The subjects preferred to select the circle that was partially displayed in the blind spot, i.e. not the one that they could actually see one hundred percent. When the various visual sensory impressions are compared in the brain, the visual information interpreted by the brain itself obviously enjoys a higher level of trustworthiness than that of the sensory stimulus actually seen.
Grabot, Laetitia & Kayser, Christoph (2020). Alpha Activity Reflects the Magnitude of an Individual Bias in Human Perception. The Journal of Neuroscience, doi: 10.1523 / JNEUROSCI.2359-19.2020.
Stephani, T., Waterstraat, G., Haufe, S., Curio, G., Villringer, A. & Nikulin, V. V. (2020). Temporal signatures of criticality in human cortical excitability as probed by early somatosensory responses. Journal of Neuroscience, doi: 10.1523 / JNEUROSCI.0241-20.2020.
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