Differential Cutaneous Thermal Sensitivity in Humans: Method of Limit vs. Method of Sensation Magnitude

Introduction: The method of limits (MLI) and method of level (MLE) are commonly employed for the quantitative assessment of cutaneous thermal sensitivity. Thermal sensation and thermal comfort are closely related and thermal sensations evoked from the peripheral thermoreceptors play an important role in thermoregulatory response to maintain normal body temperature. The purpose of this study was to compare the regional distribution of cutaneous warm and cold sensitivity between MLI and the method of sensation magnitude (MSM). Method: Twenty healthy men completed MLI and MSM to compare the regional distribution of cutaneous warm and cold sensitivity in the thermal neutral condition. The subjects rested on a bed in a supine position for 20 min. Next, the cutaneous thermal sensitivity of ten body sites was assessed by the means of MLI and MSM for both warmth and cold stimuli. Results: The absolute mean heat flux in MLI and thermal sensation magnitude in MSM showed significantly greater sensitivity to cold than to warm stimulation (p < 0.01), together with a similar pattern of regional differences across ten body sites. Both sensory modalities indicated acceptable reliability (SRD%: 6.29–8.66) and excellent reproducibility (ICC: 0.826–0.906; p < 0.01). However, the Z-sore distribution in MSM was much narrower than in MLI, which may limit the test sensitivity for the detection of sensory disorders and/or comparison between individuals. Conclusion: The present results showed that both MLI and MSM are effective means for evaluating regional cutaneous thermal sensitivity to innocuous warm and cold stimulations to a strong degree of reliability and reproducibility.

The frequency of cortical microstimulation shapes artificial touch

Intracortical microstimulation (ICMS) of the somatosensory cortex evokes vivid tactile sensations and can be used to convey sensory feedback from brain-controlled bionic hands. Changes in ICMS frequency lead to changes in the resulting sensation, but the discriminability of frequency has only been investigated over a narrow range of low frequencies. Furthermore, the sensory correlates of changes in ICMS frequency remain poorly understood. Specifically, it remains to be elucidated whether changes in frequency only modulate sensation magnitude—as do changes in amplitude—or whether they also modulate the quality of the sensation. To fill these gaps, we trained monkeys to discriminate the frequency of ICMS pulse trains over a wide range of frequencies (from 10 to 400 Hz). ICMS amplitude also varied across stimuli to dissociate sensation magnitude from ICMS frequency and ensure that animals could not make frequency judgments based on magnitude. We found that animals could consistently discriminate ICMS frequency up to ∼200 Hz but that the sensory correlates of frequency were highly electrode dependent: On some electrodes, changes in frequency were perceptually distinguishable from changes in amplitude—seemingly giving rise to a change in sensory quality; on others, they were not. We discuss the implications of our findings for neural coding and for brain-controlled bionic hands.

Magnitude Estimation and Magnitude Production: Stimulus Frequency Effects on Magnitudes of Lingual Vibrotactile Sensation

The methods of magnitude estimation and magnitude production were employed to investigate the effects of stimulus frequency on suprathreshold lingual-vibrotactile sensation-magnitude functions. The method of magnitude estimation was used to obtain numerical judgments of sensation magnitudes for nine stimulus intensities presented to the anterior dorsum of the tongue. The vibrotactile stimulus frequencies employed for 10 subjects ( M age = 21.1 yr.) were 100, 250, and 400 Hz. The numerical responses obtained during the magnitude-estimation task were in turn used as stimuli to obtain magnitude-production values for the same three vibrotactile stimulus frequencies. The results appeared to present two suggestions. First, the effects of stimulus frequency on lingual vibrotactile-sensation magnitudes may be dependent on the psychophysical method used in any particular experiment. Second, lingual-vibrotactile magnitude-estimation scales may demonstrate asymptotic growth functions above about 25 dB sensation level. The limitation in the growth of sensation magnitude occurred for all three vibrotactile stimulus frequencies employed.

Sensation magnitude judgments are based upon estimates of physical magnitudes

After writing my response to the commentaries, I sat back and reflected on the fascination and frustration of work on this topic. There is the ancient fascination of trying to understand the nature of the sensory bridge linking us to the external world. Also, discussing the measurability of sensation brings to the surface concepts we use and take for granted when we are working in other areas of psychology; and it holds them before us for critical examination. The frustration lies chiefly in the difficulty of formulating concepts clearly, in a way understood by all. At least when constructing the original Tower of Babel, workers hearing strange words knew that communication was not occurring. The psychophysical Tower of Babel sometimes has workers using the same words, but with different meanings. Much of my response is based on attempts to clarify concepts and clear up confusions.