A massively asynchronous, parallel brain

Abstract

Whether the visual brain uses a parallel or a serial, hierarchical, strategy to process visual signals, the end result appears to be that different attributes of the visual scene are perceived asynchronously—with colour leading form (orientation) by 40 ms and direction of motion by about 80 ms. Whatever the neural root of this asynchrony, it creates a problem that has not been properly addressed, namely how visual attributes that are perceived asynchronously over brief time windows after stimulus onset are bound together in the longer term to give us a unified experience of the visual world, in which all attributes are apparently seen in perfect registration. In this review, I suggest that there is no central neural clock in the (visual) brain that synchronizes the activity of different processing systems. More likely, activity in each of the parallel processing-perceptual systems of the visual brain is reset independently, making of the brain a massively asynchronous organ, just like the new generation of more efficient computers promise to be. Given the asynchronous operations of the brain, it is likely that the results of activities in the different processing-perceptual systems are not bound by physiological interactions between cells in the specialized visual areas, but post-perceptually, outside the visual brain.

Frequency‐dependent tACS modulation of BOLD signal during rhythmic visual stimulation

“…But there is a time lag between E‐prime execution and its evoked neuronal response in visual cortex, which consists of the time delay between E‐Prime execution and flicker showed by the projector (35 ms, measured in our stimulation system), the time of retinal response to light stimulation and the conduction delay from retinal to visual cortex. The total time lag is about 65 milliseconds (Bair, ; Dalal, Westner, Bailey, Dietz, & Popov, ; Zeki, ), which is comparable to the stimulation period. This time lag would lead to a relative phase between tACS and flicker response.…”

“…Alpha amplitudes in the occipital-parietal cortex have been shown to negatively correlate with BOLD signal changes (Goldman, Stern, Engel, & Cohen, 2002;Laufs et al, 2003). If the modulation effect of 8 Hz tACS was generated through interaction with alpha oscillation, it would decrease the flicker- (Bair, 1999;Dalal, Westner, Bailey, Dietz, & Popov, 2017;Zeki, 2015), which is comparable to the stimulation period. This time lag would lead to a relative phase between tACS and flicker response.…”

The Feature Parallelism Model of Visual Recognition

“…In spite of that, hierarchal/ serial processing within major pathways is widely adopted by modern computer vision algorithms [11,[1][2]. Nowadays, scientists believe that our brains are massively parallel biological devices, even within the previously thought to be as highly serial areas ( Figure 3) [9], [10] and [12]. (a) The classical picture of a single hierarchical chain with two (or more) nodes and a terminal node (in pink) at which activity becomes perceptually explicit (needs no further processing).…”

Getting It Together: Psychological Unity and Deflationary Accounts of Animal Metacognition

“…Whether or not the brain is a massively asynchronous, parallel system, the timing of events in it is critical to understand its workings (Zeki 2015). Many animal beliefs and desires come and go quickly; they do not persist in the animal's brain for a long period of time.…”