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    Tangible Feelings, Symposium on EEG/biofeedback, iMal center for digital cultures and technology, Brussels, 16-18 September 2011

Staalhemel in Bozar documented

This video focuses on the experience of the visitor. Different facial expressions reveal inner reflections of visitors that are in interaction with the machine.

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visualisation: alpha and absence of alpha waves

This is what the plotting of data for alpha waves looked like in version 1 of the Max/MSP interface for the Staalhemel project.

data plotting for a running average of alpha waves

In the event windows on the left you see 3 windows with graphs colored (mainly) in red. The top window doesn’t show much information here; peaks will appear if there is synchronization in maximum values for alpha waves between both hemispheres. The middle window shows peaks of alpha waves over time. Color switches between red and black for each new visitor. The bottom graph reports the absence of alpha waves, which functions as an indicator of beta waves. The first version of the IMEC software did not deliver beta waves, but indicated if there was an absolute absence of alpha. This allowed me to infer moments of concentration (and the appearance of beta waves).

On the ‘frequency’ matrix display in the main window you see which steel segments are activated. This matrix represents the whole Staalhemel installation with a video window of 6 by 12 pixels (segments): the darker pixels indicate longer intervals between impacts for a particular plate. If they are white they are hammering at maximum speed (interval of 40 ms) and if they’re black they are off. The screenshot here shows a moment of concentration and the immediate response in activation of steel segments. You can see that just before this moment there was a sustained period of concentration, only interrupted by rather small amounts of alpha waves. This happened when I was working on the software while wearing the EEG headset and it tells how I was (minimally) distracted 4 times in that thinking process.

At STRP Festival in Eindhoven this version was installed for the last time.
The first day of the festival I did a testrun of the new software, Staalhemel version 2. In this update alpha and beta wave information for 8 channels is visualised. Due to certain limits and interferences this 8-channel version is not fully operational yet. This version maps the layout of your head to the installation matrix: front panel rows represent left and right frontal area of your brain, next rows show results from the side electrodes and top and back of the head are translated to the last rows of steel plates.

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conversation experiment 1

On the picture above you see graphs of alpha wave levels (relaxation) and beta wave levels (focus) from all electrodes on the headset. You see left and right for alpha and then left and right for beta on each row. See my previous post on brain functions to understand the positions on the scalp from which these recordings were taken. Basically the order from top to bottom reflects the orientation from front of head to back of head. This experiment consisted of making a phone call and have a conversation while registering my brain waves.

On the plotting of data from the left prefrontal electrode you clearly see a decrease in alpha wave values corresponding with a block of sustained peak values in beta (blue circles). This is quite an extreme example in the recording of cognitive concentration to perform the task of conversing, formulating questions and answering to the other party’s questions. The alpha waves show a majority of values under 10%, whereas the peak values in beta show values over 30% (percentages are measured differently for beta than for alpha but in my plotting all percentages are scaled respectively to a range between 1 and 10). Alpha values for the right prefrontal area are inconclusive with values centering around an average. The beta values for the same area however (top right window), are very significant in a totally different way from peaking at maximum. In this window you see how a repetitive pattern of sustained identical values is established. This pattern also shows when the test subject is writing or reading e-mail. This type of block iteration can be monitored on several windows and can be considered significant for the occurrence of an event, which in this case means the act of getting information – while talking on the phone to my wife – about how my daughter is doing in daycare.

Another striking data profile is found on the occipital electrodes at the back of the head where the visual cortex resides (green circles). Again alpha is decimated, especially on the right channel, and simultaneously the beta window shows sustained peaks (and a lot of separate peaks on the left side). The orange circle shows you there’s a difference between left and right vision, since peaks start with a different timing. At present I don’t have enough test results to make conclusions as to why beta values for visual processing are elevated here.

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brain functions

The first version of Staalhemel was based on a general, averaged measurement of alpha wave levels. In 2010 I’m investigating with researcher Lindsay Brown from Holst Centre in Eindhoven how we can interpret the discrete measurements of the eight individual electrodes on the headset. The electrode positions are named FP1, FP2, F7, F8, C3, C4, O1 and O2.

FP1 covers Brodmann area 10 on the front left side of the frontal lobe. This is part of the prefrontal cortex, that highly developed part of the brain which sets us apart from other mammals since it is responsible for the execution of cognitive tasks. Complex behaviours and simultaneous mental activities need a kind of working memory that keeps track of running tasks in either pending states or executive states. For most cognitive functions information needs to be retrieved after completion of another task. The prefrontal cortex co-ordinates all of this mental traffic and shows clear elevation in beta levels when performing calculative tasks, logical puzzles or other intellectual questions. FP2 covers the right side of the prefrontal cortex.

F7 and F8 cover parts of the frontal cortex. The frontal cortex is involved in integrating sensory information with data retrieval from memory locations. This way new sensory information can be compared with earlier perceptions. Area 45 – which is one part of Broca’s area, a brain centre dedicated to language production – at position F8 is also believed to recover semantic information and to evaluate that information in the light of the current context.

C3 and C4 are located on top of the primary somatosensory cortex, in the parietal part of the cortex. This is a clearly defined strip on top of the brain responsible for processing touch and sensation as well as keeping track of the location of your body parts (proprioception).

The two electrodes at the back of the headset, O1 and O2 for the occipital area of the cortex, cover the secondary visual cortex which is processing information relating to visual association. Cells are tuned to simple properties such as orientation, spatial frequency, and color. Depending on the exact positioning of the headset – which is likely to be slightly different per individual – they might also track the primary visual cortex from which the information is forwarded to the secondary visual cortex. Primary cortex here corresponds to Brodmann area 17 and the secondary to area 18. The connectivity between primary and secondary cortices is important for visual memory.

Table to check which Brodmann area corresponds to which electrode position

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audio recordings

Staalhemel music samples by audiostore

Audio recordings of Staalhemel as a percussive machine are now available on Soundcloud. Some tracks were part of the concert version of Staalhemel which took place on April 24th in Happy New Festival. Select a track and press play in the widget above.

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Staalhemel audio

(c) Gregoir Nieuwenhuyse

Below you find the first sample that was made available of Staalhemel as a percussive machine. The concert version took place on 24 April 2010 in Happy New Festival, Kortrijk, Belgium.

Impact – binaural mic by audiostore

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musical interface

musical interface for Staalhemel

musical interface for Staalhemel

Preparing the musical interface in Max/MSP to control the Staalhemel installation as a percussive apparatus. On the opening of the Sound Art expo at Festival van Vlaanderen Kortrijk the premiere will take place of this concert version. In the concert version De Boeck will operate the 80 steel tiles manually via a touchscreen while his brainwaves will operate other musical parameters.

Concert:  24 april, Budascoop, Kortrijk (B) – 20:15

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New Media Prize nomination

Nieuwe Media Prijs

‘Staalhemel’ has been shortlisted for the New Media Prize awarded by the Liedts-Meesen Foundation. The selected works will be shown in ‘Update III’, the third bi-annual for interactive and digital art organized by Zebrastraat in Gent, Belgium. For this exhibition that runs from 16 April to 20 June Christoph De Boeck will create a smaller version of the steel sky. Meanwhile, people can also visit the big version in Kortrijk from 25 April to 9 May.

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Video images

Some video images from the first public presentation of ‘Staalhemel’

Staalhemel – Steel Sky from Christoph De Boeck on Vimeo.

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dorkbot presentation

On October 28, 2009 Christoph De Boeck presented notes on the creation process of ‘Staalhemel’ at dorkbotBRU at iMal in Brussels, a gathering of technologically minded artists and interested spectators. This session was recorded and can be watched here:

Still from the presentation at dorkbotBRU

Still from the presentation at dorkbotBRU

Or via this link:


Info on dorkbot and other meetings at iMal:


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