Fig. 1

(a) Concept of funneling illusion and rule of determining \(\beta\). \(\phi _1\) and \(\phi _2\) is the actuator intensity of each CH1 and CH2. (b)-(c) Relationship between \(\beta\) and intensity of CH1 and CH2 with (b) vibrotactile and (c) electrotactile modality for a representative participant. Since both actuators’ perceived intensities at the reference intensities (\(\psi _{\textit{REF}_1}\) and \(\psi _{\textit{REF}_2}\)) are set to be the same for each modality, the actuator intensities at the reference intensities (\(\phi _{\textit{REF}_1}\) and \(\phi _{\textit{REF}_2}\)) may differ. (Dotted line: CH1, Solid line: CH2).