processing without attention and consciousness

From Scholarpedia

Curator: Dr. Naotsugu Tsuchiya, California Institute of Technology, Pasadena, CA, USA
Curator: Dr. Christof Koch, Division of Biology, Caltech, Pasadena, CA

Processing without top-down attention and consciousness

Rapid visual categorization

Visual input can be classified very rapidly. As famously demonstrated by Thorpe and colleagues (Thorpe et al., 1996; Kirchner and Thorpe, 2006) around 120 msec following image onset, some brain processes begin to respond differentially to images containing one of more animals from pictures than contain none. At this speed, it is no surprise that subjects often respond without having consciously seen the image (VanRullen et al., 2001; VanRullen and Koch, 2003); consciousness for the image may come later or not at all.

Dual-task and dual-presentation paradigms support the idea that such discriminations can occur in the near-absence of focal, spatial attention (Li et al., 2002 Attention and Consciousness/How to Manipulate Attention; Rousselet et al., 2002), (but see (Einhauser et al., 2007)) implying that purely feed-forward networks can support complex visual decision-making in the absence of both attention and consciousness (VanRullen et al., 2001; VanRullen and Koch, 2003). Indeed, this has now been formally shown in the context of a purely feed-forward computational model of the primate’s ventral visual system (Serre et al., 2007).

Animal experiments could substantiate this assertion. Imagine that all the cortico-cortical pathways from prefrontal cortex back to higher level visual cortex and from there on even further back to primary and secondary visual cortices could be transiently knocked out using a molecular silencing tool (without compromising feed-forward processing). That is, for a couple of hours, the brain of the monkey would only support feed-forward pathways. It is quite likely that such an animal could still carry out a previously learned simple discrimination task with the same level of performance as prior to the intervention (upper left quadrant in Table 1 Attention and Consciousness), without any top-down attention (since prefrontal cortex would have no means to modulate the processes in the visual brain), and possibly without conscious perception (although this latter would be difficult to demonstrate in an animal preparation).

References

• Einhauser W, Mundhenk TN, Baldi P, Koch C, Itti L (2007) A bottom-up model of spatial attention predicts human error patterns in rapid scene recognition. Journal of Vision 7:1-13.
• Kirchner H, Thorpe SJ (2006) Ultra-rapid object detection with saccadic eye movements: visual processing speed revisited. Vision Res 46:1762-1776.
• Li FF, VanRullen R, Koch C, Perona P (2002) Rapid natural scene categorization in the near absence of attention. Proc Natl Acad Sci U S A 99:9596-9601.
• Rousselet GA, Fabre-Thorpe M, Thorpe SJ (2002) Parallel processing in high-level categorization of natural images. Nat Neurosci 5:629-630.
• Serre T, Oliva A, Poggio T (2007) A feedforward architecture accounts for rapid categorization. Proc Natl Acad Sci U S A 104:6424-6429.
• Thorpe S, Fize D, Marlot C (1996) Speed of processing in the human visual system. Nature 381:520-522.
• VanRullen R, Koch C (2003) Visual selective behavior can be triggered by a feed-forward process. J Cogn Neurosci 15:209-217.
• VanRullen R, Delorme A, Thorpe SJ (2001) Feed-forward contour integration in primary visual cortex based on asynchronous spike propagation. Neurocomputing 38:1003-1009.

Invited by:	Dr. Anil K Seth, University of Sussex, UK
Action editor:	Dr. Eugene M. Izhikevich, Editor-in-Chief of Scholarpedia, the peer-reviewed open-access encyclopedia
Action editor:	Dr. Anil K Seth, University of Sussex, UK
Assistant editor:	Mr. Srivas Chennu, PhD Student, Computing Laboratory, University of Kent, Canterbury, U.K.
Reviewer B:	Dr. Susana Martinez-Conde, Barrow Neurological Institute, Phoenix, AZ
Reviewer C:	Dr. Lawrence M. Ward, University of British Columbia, Vancouver, CANADA