Feed: ScienceDirect Publication: Brain and Cognition
Posted on: dinsdag 30 november 2010 7:13
Author: ScienceDirect Publication: Brain and Cognition
Subject: ERP evidence of visualization at early stages of visual processing
Publication year: 2010 |
Suggested by Maarten
Feed: Psychological Science RSS feed -- Preview Articles
Posted on: 23 November 2010 21:08
Author: Rosenthal, O., Humphreys, G. W.
Subject: Perceptual Organization Without Perception: The Subliminal Learning of Global Contour
| A critical step in visual perceptual processing is integrating local visual elements into contours so that shapes can be derived from them. It is often assumed that contour integration may reflect hardwired coding of low-level visual features. In this study, we present novel evidence indicating that integration of local elements into contours can be learned subliminally, despite being irrelevant to the training task and despite the local properties of the display varying randomly during training. Learning occurred only when contours were consistently paired with task-relevant targets—echoing the findings of previous studies on subliminal learning of low-level features. Our data indicate that task-irrelevant, exposure-based learning extends beyond local low-level visual features and may play a critical role at multiple levels of visual perceptual organization. |
| "Rond tien uur doken we met een lawaaierige bende acht- tot dertienjarigen een aula van de Oude Valk in, benieuwd naar wat professor in de experimentele psychologie Johan Waegemans ons daar een uur lang zou vertellen over "kijken met je hersenen". Lang geleden dat wij een aula nog zo tot de nok vol hadden gezien. Lang geleden dat wij zoveel vlijt en ongeremdheid bijeen zagen..." http://www.veto.be/veto/veto3706/KIND.html |
The perception of global form requires integration of local visual cues across space and is the foundation for object recognition. Here we used magnetoencephalography (MEG) to study the location and time course of neuronal activity associated with the perception of global structure from local image features. To minimize neuronal activity to low-level stimulus properties, such as luminance and contrast, the local image features were held constant during all phases of the MEG recording. This allowed us to assess the relative importance of striate (V1) versus extrastriate cortex in global form perception.
Methodology/Principal FindingsStimuli were horizontal, rotational and radial Glass patterns. Glass patterns without coherent structure were viewed during the baseline period to ensure neuronal responses reflected perception of structure and not changes in local image features. The spatial distribution of task-related changes in source power was mapped using Synthetic Aperture Magnetometry (SAM), and the time course of activity within areas of maximal power change was determined by calculating time-frequency plots using a Hilbert transform. For six out of eight observers, passive viewing of global structure was associated with a reduction in 10–20 Hz cortical oscillatory power within extrastriate occipital cortex. The location of greatest power change was the same for each pattern type, being close to or within visual area V3a. No peaks of activity were observed in area V1. Time-frequency analyses indicated that neural activity was least for horizontal patterns.
ConclusionsWe conclude: (i) visual area V3a is involved in the analysis of global form; (ii) the neural signature for perception of structure, as assessed using MEG, is a reduction in 10–20 Hz oscillatory power; (iii) different neural processes may underlie the perception of horizontal as opposed to radial or rotational structure; and (iv) area V1 is not strongly activated by global form in Glass patterns.
