Journal of Rehabilitation Medicine 51-3 | Page 68

214 U. Wijk et al. longer learning period and also 2 occasions per day during the first week, which indicates that the subjects learn even faster and within a day. The learning could even have a “3-occasion-effect” with at least 3 h in bet- ween occasions. In our study we used mechanotactile stimuli, which has been proven to be easy to interpret for sensory feedback (24). Mechanotactile is also a more common modality to receive as sensory feedback in daily use compared with vibrotactile or electrotactile stimuli, which was used by Chai et al. (27). The very good agreement between stimuli and responses in our study indicates that it is possible to learn predefined areas on the forearm skin that is comparable to referred sensation in capacity to localize the predefined areas. Chai et al. (27) show similar results, and non-soma- totopically matched areas reached comparable levels to the somatotopically matched areas considering re- sponse time from the actual stimulation to the response of the perceived stimulation, during those 3 training days (27). Our result opens up for the possibility for amputees without referred sensations, as well as for congenital amputees, to learn the association and keep it prolonged for at least 2 weeks. Compared with our experimental learning set-up, prosthesis users would probably wear a prosthesis with sensory feedback more frequently and therefore get more confident with the sensory associations. Learning as a concept is defined as an encoding of memory and is the process of “gradual changes in behavior as a function of training” (31). In the dual code theory there are separate “channels” to process information from different senses. Therefore, multiple senses should be used to facilitate learning, without exposing the working memory to fatigue (32). Three learning styles for adults are described; visual, auditory and kinesthetic, and the best learning is achieved when these 3 approaches are combined (33). In our study we apply visual and kinaesthetic (sensory) information at the same time, and in accordance with the dual code theory and the 3 learning styles this should ease the learning. A well-known concept in psychology and cognitive literature is the spacing effect (34). The spacing effect implies that practice is spread over a period of time and the opposite is when practice is massed at one or few close occasions. When the same amount of time is spent practicing, learning is most effective when spaced over time (34, 35). The memory tends to last longer, since spaced learning keeps new cells maintained (36). It has also been shown that the best learning occurs when the practice intervals were expanding over time (37). In the current study the spacing effect was applied and the occasions were spaced over a period of 5 weeks. In the first week the training occasions were made twice a day, the second www.medicaljournals.se/jrm week the training was made once a day and there was an interval of 1 week made respectively for the last 2 occasions. Another concept used in research for lear- ning and memory is the testing effect. The effect in long-term memory is better when memory tests are made during the period of practice (38). In the present study every learning occasion included both a pure learning session and testing session where the subject received feedback on the responses. This may have been advantageous for learning. No difference was seen in learning over time bet- ween the sexes. However, the group of men was small, only 6 men participated compared with 25 women, and the lack of statistical significant difference may be due to lack of statistical power. The results did not show any differences between the different age groups. The U-shape of the tactile display imitates the order and positions of the fingers and may ease the intuitive interpretation of the stimuli of the predefined area with the specific finger. The middle finger was easiest to discriminate, whereas the little finger stimulation was most frequently mistaken, and instead associated with being the ring finger. A possible explanation for this is the U-shape. The stimulation for the middle finger was applied over the flexor tendons to the fingers and the median nerve, and some of the subjects reported a different sensation (tingling), or a stronger sensation of the stimulations of the area for the middle finger compared with stimulations of the other finger areas. The middle finger stimulation was applied in the centre and the most distally on the forearm and might have become a reference for the other stimulated areas which were either on the one or the other side of the middle finger. There was barely any misperception between the stimulations on different side of the middle finger (digit 1↔digit 4), (d1↔d5), (d2↔d4) and (d2↔d5), but it was more difficult to discriminate adjacent fingers (d1↔d2) and (d3↔d4). Nerve innervation is a possible explanation, the 3 radial sites (d1, d2 and d3) were applied to skin that is innervated by the median nerve, and the 2 ulnar sites (d4 and d5) were applied on skin innervated by the ulnar nerve. Study limitations Stimulation on the forearm comprised pressure from servo motors, and it is impossible to avoid mechanical noise. Since the speed of rotation of the servo motor was set to be the same, when applying pressure on the pre-defined area on the forearm, the 5 servo motors should sound similar. However, some subjects noticed that some servo motors could slightly differentiate in sound, which may have affected the performance in the progression of learning. According to dual code theory, the involvement of more senses can facilitate learning.