Biology subjects

Tommerdahl, M.

Publications and source records attributed to Tommerdahl, M..

2 recordsLinked to original sources

bioRxiv2019

Accuracy of different modalities of reaction time testing: Implications for online cognitive assessment tools.

Reaction time testing is widely used in computerized cognitive assessments, and clinical studies have repeatedly shown it to be a sensitive indicator of cognitive function. Typically, the reaction time test is administered by presenting a subject with a visual stimulus on a computer monitor and prompting the individual to respond (via keypad or computer mouse) as quickly as possible. The individuals reaction time is calculated as the interval between presentation of the stimulus and the time recorded from the mechanical response. However, there are many inherent latencies and variabilities that may be introduced to the measure by both hardware (computer monitor and mouse) and software (operating system). Because of these delays, we hypothesized that a comparison of hardware protocols (excluding human response) would demonstrate significant differences in the resulting reaction time measures. To simulate the delays of various components of the common systems used to obtain reaction time, we conducted a simple experiment in which either a visual or tactile stimulus evoked a movement from a mechanical transducer to respond to a computer peripheral or a dedicated response device. In the first condition, a simulated visual reaction time test was conducted by flashing a visual stimulus on a computer monitor. The stimulus was detected by a dedicated light sensor, and a linear actuator delivered the mechanical response via computer mouse. The second test condition employed a mobile device as the medium for the visual stimulus, and the mechanical response was delivered to the mobile devices touchscreen. The third and fourth test conditions simulated tactile reaction time tests in which the stimulus was generated by a dedicated hardware device. The third condition simulated a tactile stimulus, which was detected by a mechanical switch, and again a hardware device delivered the response via computer mouse. The fourth condition also simulated a tactile stimulus, but the response was delivered by a dedicated hardware device designed to store the interval between stimulus delivery and stimulus response. There were significant differences in the range of responses recorded from the four different conditions with the reaction time collected from a visual stimulus on a mobile device being the worst and the device with dedicated hardware designed for the task being the best. The results suggest that some of the commonly used visual tasks on consumer grade computers could be introducing significant errors for reaction time testing and that dedicated hardware designed for the reaction time task is needed to minimize testing errors.

bioengineering↗

bioRxiv2019

Multimodal frequency representations are embedded in modality-defined cortical sensory systems

Sensory information is represented and elaborated in hierarchical cortical systems that are thought to be dedicated to individual sensory modalities. This traditional view of sensory cortex organization has been challenged by recent evidence of multimodal responses in primary and association sensory areas. Although it is indisputable that sensory areas respond to multiple modalities, it remains unclear whether these multimodal responses reflect selective information processing for particular stimulus features. Here, we used fMRI adaptation to identify brain regions that are sensitive to the temporal frequency information contained in auditory, tactile, and audiotactile stimulus sequences. A number of brain regions distributed over the parietal and temporal lobes exhibited frequency-selective temporal response modulation for both auditory and tactile stimulus events, as indexed by repetition suppression effects. A smaller set of regions responded to crossmodal adaptation sequences in a frequency-dependent manner. Despite an extensive overlap of multimodal frequency-selective responses across the parietal and temporal lobes, representational similarity analysis revealed a cortical \"regional landscape\" that clearly reflected distinct somatosensory and auditory processing systems that converged on modality-invariant areas. These structured relationships between brain regions were also evident in spontaneous signal fluctuation patterns measured at rest. Our results reveal that multimodal processing in human cortex can be feature-specific and that multimodal frequency representations are embedded in the intrinsically hierarchical organization of cortical sensory systems.\n\nSignificance StatementA hallmark of traditional brain organization models is the segregation of signals from the different senses in modality-dedicated brain regions. Recent evidence showing multimodal activity in brain regions thought to be dedicated to a single modality have challenged the traditional sensory cortex model. Notably, few studies have explored the feature-specificity of multimodal responses found in sensory cortex. Here, we used fMRI adaptation to identify parietal and temporal cortex regions which exhibited sensitivity to both tactile and auditory frequency information. These univariate results demonstrate that multimodal processing in sensory cortex can be feature-specific. Using the same data, though, we found clear evidence of modality-based cortical organization estimated from multivariate response patterns and spontaneous BOLD signal fluctuations. Thus, our results reveal an embedding of feature-specific multimodal processing in traditionally-defined cortical systems.

neuroscience↗