Biomedical subjects

Mika Koivisto

Publications and source records attributed to Mika Koivisto.

17 recordsLinked to original sources

PubMed2007

Pulsed and continuous wave mobile phone exposure over left versus right hemisphere: effects on human cognitive function.

The possible effects of continuous wave (CW) and pulse modulated (PM) electromagnetic field (EMF) on human cognition was studied in 36 healthy male subjects. They performed cognitive tasks while exposed to CW, PM, and sham EMF. The subjects performed the same tasks twice during each session; once with left-sided and once with right-sided exposure. The EMF conditions were spread across three testing sessions, each session separated by 1 week. The exposed hemisphere, EMF condition, and test order were counterbalanced over all subjects. We employed a double-blind design: both the subject and the experimenter were unaware of the EMF condition. The EMF was created with a signal generator connected via amplifier to a dummy phone antenna, creating a power output distribution similar to the original commercial mobile phone. The EMF had either a continuous power output of 0.25 W (CW) or pulsed power output with a mean of 0.25 W. An additional control group of 16 healthy male volunteers performed the same tasks without any exposure equipment to see if mere presence of the equipment could have affected the subjects' performance. No effects were found between the different EMF conditions, separate hemisphere exposures, or between the control and experimental group. In conclusion, the current results indicate that normal mobile phones have no discernible effect on human cognitive function as measured by behavioral tests.

Adult↗

PubMed2006

The electrophysiology of introspection.

To study whether the distinction between introspective and non-introspective states of mind is an empirical reality or merely a conceptual distinction, we measured event-related potentials (ERPs) elicited in introspective and non-introspective instruction conditions while the observers were trying to detect the presence of a masked stimulus. The ERPs indicated measurable differences related to introspection in both preconscious and conscious processes. Our data support the hypothesis that introspective states empirically differ from non-introspective states.

Brain↗

PubMed2006

The role of unattended distractors in sustained inattentional blindness.

When participants are attending to a subset of visual targets or events and ignoring irrelevant distractors ("selective looking"), they often fail to detect the appearance of an unexpected visual object or event even when the object is visible for several seconds ("sustained inattentional blindness"). An important factor influencing detection rates in selective looking is the attentional set of the participant: the more similar the features of the unexpected object are to the attended ones, the more probably it will be detected. We examined the possible contribution of active ignoring to this similarity effect by studying the role of the distractor objects in sustained inattentional blindness. First we showed the similarity effect for chromatic colors and then we manipulated the similarity of the unexpected object in relation to the distractor objects and did not find any effects. Moreover, we found that inattentional blindness was present even when the displays did not contain any irrelevant to-be-ignored objects. We conclude that attending to target items on the basis of attentional set, but not active ignoring of nontargets items, is sufficient for the occurrence of sustained inattentional blindness.

Adult↗

PubMed2006

Mobile phone effects on children's event-related oscillatory EEG during an auditory memory task.

PURPOSE: To assess the effects of electromagnetic fields (EMF) emitted by mobile phones (MP) on the 1 - 20 Hz event-related brain oscillatory EEG (electroencephalogram) responses in children performing an auditory memory task (encoding and recognition). MATERIALS AND METHODS: EEG data were gathered while 15 subjects (age 10 - 14 years) performed an auditory memory task both with and without exposure to a digital 902 MHz MP in counterbalanced order. RESULTS: During memory encoding, the active MP modulated the event-related desynchronization/synchronization (ERD/ERS) responses in the approximately 4 - 8 Hz EEG frequencies. During recognition, the active MP transformed these brain oscillatory responses in the approximately 4 - 8 Hz and approximately 15 Hz frequencies. CONCLUSIONS: The current findings suggest that EMF emitted by mobile phones has effects on brain oscillatory responses during cognitive processing in children.

Adolescent↗

PubMed2006

The role of eye movements in lateralised word recognition.

The present study examined the role of eye movements and attention in lateralised word recognition, where words and pseudowords are presented to the right or left of the fixation point, and participants are asked to decide whether or not the presented letter string is a word. In the move condition, our participants were instructed to launch a saccade towards the target letter string, which was erased from the screen after 100 ms (i.e., prior to the eyes reaching the target). It was assumed that a preparation of an eye movement simultaneously with an attention shift results in the attention being more readily allocated to the target. In the fixate condition, participants were asked to fixate on the central fixation point throughout the trial. The data on response accuracy demonstrated that word recognition in the LVF benefited from a preparation to make an eye movement, whereas the performance in the RVF did not benefit. The results are consistent with the attentional advantage account (Mondor & Bryden, 1992), according to which the performance deficit of RH for verbal stimuli may be overcome by orienting attention to the LVF prior to the presentation of a letter string.

Adult↗

PubMed2005

Independence of visual awareness from the scope of attention: an electrophysiological study.

Recent brain imaging studies have revealed that increased neural activity along the ventral visual stream and parietal and frontal areas is associated with visual awareness. In order to study the time-course and temporal aspects of awareness, we examined electrophysiological correlates of conscious vision in two masking experiments. The differences in event-related potentials (ERPs) between unmasked (consciously recognized) and masked (unrecognized) stimuli were considered to be electrophysiological correlates of awareness. Two attentional conditions (global, local) were included to examine the relationship between the scope of attention and awareness. Two ERP-deflections were found to correlate with awareness. First, awareness was associated with a posterior negative amplitude shift 130-320 ms after the stimulus. This effect was present in both attention conditions, suggesting that it emerges independent of the scope of attention. Second, ERPs to unmasked stimuli became more positive as compared with masked stimuli around 400 ms, peaking at parietal sites. This effect was attenuated in the local attention condition, although the participants were aware of the stimuli, suggesting that the late positivity does not directly correlate with visual awareness. The results imply that the earlier negativity is the earliest and most direct correlate of visual awareness.

Adult↗

PubMed2005

Independence of visual awareness from attention at early processing stages.

According to a widely accepted idea, only the results of attentional selection reach visual awareness. A competing model postulates that awareness is independent of attentional selection: contents of subjective visual experience may also exist without the contribution of attention. We tested these competing models by tracking the independent contributions of selective attention and awareness to electrophysiological brain responses. Our results showed that the earliest effects of visual awareness emerged earlier than the effects of attention and regardless of the presence or absence of attention. The early effects of attention were elicited regardless of the presence or absence of awareness. The results suggest that visual awareness and selective attention are initially independent of each other.

Adolescent↗

PubMed2005

Prechange event-related potentials predict change blindness in various attention conditions.

We investigated the mechanisms of change blindness by measuring electrophysiological responses in humans to the prechange display. The change blindness paradigm included different attentional cueing (valid, invalid, no cue) conditions. The results showed that event-related potentials to the prechange display predicted change detection performance. After a valid cue, the prechange responses in detected change trials showed evidence of attentional focusing. However, in no cue and invalid cue conditions successful change detection was associated with electrophysiological responses indicating more globally distributed attention, whereas the electrophysiological pattern associated with strong attentional focusing predicted change blindness. The results suggest that specific patterns of encoding the prechange display predict change detection performance not only between different attention conditions but also within them.

Adult↗

PubMed2005

Electromagnetic field emitted by 902 MHz mobile phones shows no effects on children's cognitive function.

The present study investigated the potential effects of a standard 902 MHz global system for mobile communication (GSM) mobile phone on 10-14 years old children's cognitive function. A total of 32 children (16 boys, 16 girls) participated with their own and parental consent. The subjects were 10-14 years old (mean 12.1 years, SD 1.1). They performed a battery of cognitive tests twice in a counter-balanced order: once while exposed to an active mobile phone and once during exposure to an inactive phone. The tests were selected from those we used earlier with adults. The statistical analyses showed no significant differences between the mobile phone off and on conditions in reaction times and accuracy over all tests or in any single test. It was concluded that a standard mobile phone has no effect on children's cognitive function as measured by response speed and accuracy. The present results challenge some earlier findings suggesting that the electromagnetic field (EMF) created by an active mobile phone would facilitate cognitive functioning.

Adolescent↗

PubMed2004

Effects of electromagnetic field emitted by cellular phones on the EEG during an auditory memory task: a double blind replication study.

The effects of electromagnetic fields (EMF) emitted by cellular phones on the event related desynchronization/synchronization (ERD/ERS) of the 4-6, 6-8, 8-10, and 10-12 Hz electroencephalogram (EEG) frequency bands were studied in 24 normal subjects performing an auditory memory task. This study was a systematic replication of our previous work. In the present double blind study, all subjects performed the memory task both with and without exposure to a digital 902 MHz field in a counterbalanced order. We were not able to replicate the findings from our earlier study. All eight of the significant changes in our earlier study were not significant in the present double blind replication. Also, the effect of EMF on the number of incorrect answers in the memory task was inconsistent. We previously reported no significant effect of EMF exposure on the number of incorrect answers in the memory task, but a significant increase in errors was observed in the present study. We conclude that EMF effects on the EEG and on the performance on memory tasks may be variable and not easily replicable for unknown reasons.

Adult↗

PubMed2004

902 MHz mobile phone does not affect short term memory in humans.

We studied the effects of an electromagnetic field (EMF) as emitted by a 902 MHz mobile phone on human short term memory. This study was a replication with methodological improvements to our previous study. The improvements included multi-centre testing and a double blind design. A total of 64 subjects (32 men) in two independent laboratories performed a short term memory task (n-back) which poses a varying memory load (0-3 items) on the subjects' memory. They performed the task twice, once each under EMF and sham exposure. Reaction times (RTs) and accuracy of the responses were recorded. The order of exposure and memory load conditions were counterbalanced across subjects and gender. There were no statistically significant differences in performance between the two laboratories. We could not replicate our previous results: the EMF had no effect on RTs or on the accuracy of the subjects' answers. The inability to replicate previous findings could have been caused by lack of actual EMF effects or the magnitude of effects being at the sensitivity threshold of the test used.

Adult↗

PubMed2004

The effects of eye movements, spatial attention, and stimulus features on inattentional blindness.

Observers often fail to detect the appearance of an unexpected visual object ("inattentional blindness"). Experiment 1 studied the effects of fixation position and spatial attention on inattentional blindness. Eye movements were measured. We found strong inattentional blindness to the unexpected stimulus even when it was fixated and appeared in one of the expected positions. The results suggest that spatial attention is not sufficient for attentional capture and awareness. Experiment 2 showed that the stimulus was easier to consciously detect when it was colored but the relation of the color to the color of the attended objects had no effect on detection. The unexpected stimulus was easiest to detect, when it represented the same category as the attended objects.

Adult↗

PubMed2003

Effect of a 902 MHz electromagnetic field emitted by mobile phones on human cognitive function: A replication study.

Our study was a replication and extension with methodological improvements to a previous study on effects of the electromagnetic field (EMF) emitted by a 902 MHz mobile phone on human cognitive functioning. Improvements on the previous study included multicentre testing and a double blind design. A total of 64 subjects (32 men and 32 women) in two independent laboratories performed a battery of 9 cognitive tasks twice: while the EMF was on and while it was off. Reaction times (RTs) and accuracy were recorded. The order of exposure and tasks was counterbalanced across subjects and gender. There were no statistically significant differences in performance between genders or laboratories. Although the RTs and the accuracy of answers were very similar to those of our previous study, our previous results were not replicated. We concluded that EMF had no effect on RTs or on the accuracy of the subjects' answers. Further, our results indicate that our EMF had no immediate effect on human cognitive functioning or that such effects are so small that they are observed on behavior only occasionally.

Adult↗

PubMed2003

Interhemispheric categorization of pictures and words.

Earlier studies suggest that interhemispheric processing increases the processing power of the brain in cognitively complex tasks as it allows the brain to divide the processing load between the hemispheres. We report two experiments suggesting that this finding does not generalize to word-picture pairs: they are processed at least as efficiently when processed by a single hemisphere as compared to processing occurring between the two hemispheres. We examined whether dividing the stimuli between the visual fields/hemispheres would be more advantageous than unilateral stimulus displays in the semantic categorization of simultaneously presented pictures, words, and word-picture pairs. The results revealed that within-domain stimuli (semantically related picture pairs or word pairs) were categorized faster in bilateral than in unilateral displays, whereas cross-domain stimuli (word-picture pairs) were not categorized faster in bilateral than in unilateral displays. It is suggested that interhemispheric sharing of word-picture stimuli is not advantageous as compared to unilateral processing conditions because words and pictures use different access routes, and therefore, it may be possible to process in parallel simultaneously displayed word-picture stimuli within a single hemisphere.

Adult↗

PubMed2003

An ERP study of change detection, change blindness, and visual awareness.

Electrophysiological correlates of change detection and change blindness were studied in 12 observers. The ERP difference between detected changes and undetected changes was considered an electrophysiological correlate of visual awareness. Two distinct electrophysiological responses correlated with the awareness of change. First, awareness was associated with a negative amplitude shift at posterior sites around 200 ms after the change in the stimulus. The latency of the negative shift varied as a function of the task difficulty and the speed of becoming aware of the change. Second, ERPs to detected changes became more positive as compared with undetected changes around 400 ms after the change in the stimulus, peaking at parietal sites. We suggest that the earlier negativity is associated with a change in the content of visual awareness, whereas the later positivity may reflect more global processes needed in decision making and action planning.

Adult↗

PubMed2002

Conscious and unconscious uses of memory in multiple sclerosis.

Conscious and unconscious uses of memory and priming were studied in 30 patients with multiple sclerosis (MS) and 15 normal control (NC) subjects. MS patients were classified into two subgroups according to their cognitive status; 15 of them were cognitively deteriorated (the MS-D group) and 15 cognitively preserved (the MS-P group). A process dissociation procedure [J. Mem. Lang. 30 (1991) 513] was used to separate conscious and unconscious memory performance in a word stem completion task. The results showed that the MS-D group had deficient conscious memory performance, but had intact unconscious memory as well as priming. The MS-P group showed normal conscious and unconscious uses of memory and priming. Thus, in MS-related cognitive decline, conscious memory seems to be vulnerable, whereas unconscious memory remains intact. The results provide neuropsychological support for the distinction between conscious and unconscious memory processes. Moreover, the results show the importance of studying cognitively homogenous MS groups as opposed to heterogenous ones, in order to find the underlying mechanisms of memory deficits in MS. Interestingly, the neural systems needed for the unconscious use of memory do not seem to deteriorate even in MS patients with deficient overall cognitive capacity. This finding encourages the development of future rehabilitation programs, suggesting that unconscious remembering might help MS patients with deficient conscious memory to cope with their daily activities.

Adult↗

PubMed2002

Hemispheric semantic priming in the single word presentation task.

Functional brain asymmetries in semantic activation were studied by presenting categorically related (e.g. TABLE-BED) or unrelated primes and targets to the left visual field (LVF)/right hemisphere or to the right visual field (RVF)/left hemisphere in the single word presentation lexical decision task. The results showed that the primes in the RVF/left hemisphere primed lexical decisions to the targets both in the RVF and in the LVF. However, the primes in the LVF/right hemisphere did not induce any priming in the LVF or RVF. These results suggest that the left hemisphere automatically activates categorically related meanings in both hemispheres. The role of the right hemisphere in automatic semantic processing may be very limited.

Adult↗