Data Acquisition & Analysis

Behavioural & Psychological Measures
Accuracy and reaction time (RT) indices were derived from the discrimination task as the percentage of total targets responded to and the mean time taken to respond to these targets respectively. The first four stimuli from each three-minute task were excluded from the above measures to reduce variability due to confounding effects related to task recommencement. The AD-ACL (Thaya, 1967) consists of 20 words that describe mood or feelings. Subjects rate the degree to which these adjectives describe their mood at that particular point in time on a four-point Likert-scale. Items relate to the adjectives ‘calm’, ‘excited’, ‘tired’, ‘tense’, and average to form an ‘activation’ scale (low scores represent high activation levels). A difference score was computed from this scale (i.e. ‘condition minus pre-experiment score’) and used as a dependent measure (this will be referred to as ‘Activation’).

Electrophysiological measures
EEG data were collected from 19 scalp sites (Fp1, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, O2) using an electrode cap with tin electrodes and referenced to linked ears (AMLABII acquisition system). Electro-oculographic data were recorded using tin electrodes above and below the left eye, and on the outer canthus of each eye. Data were continuously sampled at 512 Hz with a 0.05 to 120 Hz bandpass. Impedances were kept below 5 kOhm. Data were grouped into the following scalp regions: front left (FL) = mean [FP1, F3, F7]; front midline (FM) = Fz; front right (FR) = mean [FP2, F4, F8]; centre left (CL) = mean [C3, T3]; centre midline (CM) = Cz; centre right (CR) = mean [C4, T4]; posterior left (PL) = mean [T5, P3, O1]; posterior midline (PM) = Pz; posterior right (PR) = mean [T6, P4, O2].

Resting EEG: For each 2-minute resting EEG period, the 30-90 second period was EOG-corrected (Semlitsch et al., 1986), divided into 2 s bins, Fast Fourier transformed (10% cosine window) and averaged. Dependent variables were resultant EEG amplitude values grouped into five frequency bands: 1 to 4 Hz (delta); 4 to 8 Hz (theta); 8 to 12 Hz (alpha); 12 to 30 Hz (beta); 30 to 45 Hz (gamma). These will collectively be referred to as ‘FFT’.

Discrimination Task: For each 3-minute discrimination task, data were EOG-corrected (Semlitsch et al., 1986), epoched –1500 to 1000 ms post-stimulus, and the phase-locked component (mean) of these epochs computed for the target and non-target stimuli separately, for each of the frequency bands defined above for FFT data (12 dB/octave roll-off; zero phase shift). Dependent measures for this task were peak percentage power change (relative to the –1000 to –500 ms baseline) in the early sensory phase-locked response (0-200 ms post stimulus) for each of the frequency bands (early sensory change; ESC).

Statistical analyses
Results for the MP versus CONTROL comparison have been reported elsewhere (Croft et al., in press) and will not be addressed here. However, to allow the reader to compare those results to that of the present paper, relevant means and standard deviations are given in Table I, along with a brief description of the MP effect. For each of the FFT, ESC, Activation and RT measures, orthogonal repeated measures polynomial contrasts were employed to test for relations between these indices and condition (Q-Link+MP versus MP), and where appropriate, time (1st versus 2nd half of each twenty-minute condition) and scalp location (sagittal [frontal, central, posterior]; lateral [left, midline, right]). As each condition occurred 1st, 2nd and 3rd an equal number of times, for each dependent variable ‘order’ was treated as a noise variable and removed by converting scores within each order (and where appropriate frequency) to z-scores (after being transformed to normality where appropriate). To maintain appropriate alpha levels, for each of the above indices, the number of planned contrasts was restricted to the number of error degrees of freedom (Tabacknick & Fidell, 1989). Only effects due to condition or interactions between condition and topography, time or type will be reported.

To determine whether any Q-Link-related EEG changes were related to subjective state or performance measures, for the Q-Link+MP condition, correlations were performed between the sagittal, lateral and temporal dimensions of any significant contrasts, and both RT and Activation. For example, for a condition * laterality (left versus right) effect, a variable would be computed (mean left minus mean right hemisphere sites) and correlations performed between this new variable and both RT and Activation for the Q-Link+MP condition data. Non-parametric correlations were employed due to difficulties normalising data, and as two tests were performed per significant contrast, ? was reduced to 0.025.

To facilitate understanding of the effect of the Q-Link, a summary of the results from Croft et al. (in press) follows. No differences were found between the mobile phone and control condition on reaction time (p>0.45) or psychological activation (THAYA; p=0.08). In terms of resting EEG, while there was less delta power over right hemisphere sites in the control condition, this differential was accentuated in the MP condition (p=0.041), and while there was no affect of MP exposure on alpha at frontal sites, there was an enhancement of alpha over posterior sites in the EMF condition (p=0.017). Further, whereas alpha did not change over time in the CONTROL condition, it increased over time in the MP condition at midline sites (p=0.028). In relation to the phase-locked neural responses, whereas the early sensory theta response decreased over time primarily at midline sites in the CONTROL condition, this decrement was attenuated in the MP condition (p=0.038). Exposure to the active MP also caused a global reduction in the early beta response (p=0.032), with this reduction the result of an enhancement of the natural beta reduction over time that was greatest at frontal and posterior sites (p=0.035). Whereas there was no effect of the active mobile phone exposure at lateral frontal or midline posterior sites, it increased the gamma response at midline frontal and lateral posterior sites (p=0.021).

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