## 5 Validation
### Experiment A: Evaluating the Improvement in the Hit Rate Using the Haptic Tuning Fork
#### 5.1.1 Experimental Design  
This experiment was repeated twice (once with and once without the haptic tuning fork), for each of the three frequency haptic scales (with 3, 5 and 7 haptic notes). The order in performing the task, either using or not using the haptic tuning fork, was balanced between subjects to avoid any bias. Each experiment was divided into the following phases:  
Instructions: Initially, the subject reads the instructions about the experiment that includes a figure in which the user can visually observe the order and number of each haptic note within the scale. In this way, the user understands that the haptic icon with the lowest frequency corresponds to the haptic note number 1. Familiarisation: Next, the user feels all the values of a particular frequency-based haptic scale (that is, the 3, 5 or 7 values, depending on the scale). Each haptic note of the scale will be named with a number that will be simultaneously listened to during this phase. The order of appearance of the haptic icons starts with the haptic note 1 (which has the lowest frequency), followed by the haptic note 2 and so on, until showing the note with the highest frequency and then, again all the notes are reversely displayed starting with the note with the highest frequency in descending order. This phase aims to familiarise the subject with the haptic notes and their identification numbers, establishing a common language with which the user can name a particular haptic note. This phase has been designed to help the user ordering the different haptic stimuli in a natural way, using the analogy with the musical scale. Training: Once the selected scale has been haptically felt, the user will perform a training session that we will name the haptic dictation, similar to a musical dictation. The user will feel different haptic notes randomly chosen within the selected haptic scale, and he or she will have to identify them, saying their name (their associated number or position within the scale). The number of random stimuli will double the number of different values in the selected scale. Formative feedback, an audible signal, facilitates the training by indicating whether the user is right or wrong, and, in case of failure, the system tells the user which the correct note number was. This formative feedback facilitates the learning of that particular note and gives the user a reference of how far or close was his or her guess from the correct note. Though the training may be short, its main aim is to habituate users to the procedure, rather than training them thoroughly to recognise each individual stimuli. Experiment: After completing the training, the subject performs the experiment. The experiment is similar to the training but, in this case, there will not be any audio providing formative feedback. The number of random stimuli will triple the number of different values in the selected scale and the user will not know if his or her guess to identify the note is correct or not. This experiment was repeated twice for each of the three frequency-based haptic scales (once using the haptic tuning fork and once without using it). Thus, we can independently determine if the use of a frequency haptic tuning fork improves the recognition of the notes for each scale. There is a four-second lapse between one haptic note and the following one. These four seconds are composed of a second without haptic effect (zero force), 2 s with a haptic effect generated randomly (white noise) and, a final second without haptic effect. The reason for the inclusion of this haptic noise is to recreate similar conditions to the conditions when analyzing a variable using haptic feedback in a real application. When exploring complex data, not all stimuli will appear consecutively or without any other haptic information in between. During the test, we stored the number of correct haptic notes indicated by the user and, in case of failure, the distance error between the note indicated by the user and the correct note.