Back and front peripersonal space: behavioural and EMG evidence of top-down and bottom-up mechanisms

Abstract

Previous studies have identified a 'defensive graded field' in the peripersonal front space where potential threatening stimuli induce stronger blink responses, mainly modulated by top-down mechanisms, which include various factors, such as proximity to the body, stimulus valence, and social cues. However, very little is known about the mechanisms responsible for representation of the back space and the possible role of bottom-up information. By means of acoustic stimuli, we evaluated individuals' representation for front and back space in an ambiguous environment that offered some degree of uncertainty in terms of both distance (close vs. far) and front-back egocentric location of sound sources. We aimed to consider verbal responses about localization of sound sources and EMG data on blink reflex. Results suggested that stimulus distance evaluations were better explained by subjective front-back discrimination, rather than real position. Moreover, blink response data were also better explained by subjective front-back discrimination. Taken together, these findings suggest that the mechanisms that dictate blink response magnitude might also affect sound localization (possible bottom-up mechanism), probably interacting with top-down mechanisms that modulate stimuli location and distance. These findings are interpreted within the defensive peripersonal framework, suggesting a close relationship between bottom-up and top-down mechanisms on spatial representation.

Keywords: Back space; Blink reflex; EMG; Peripersonal space; Rear space.

Fig. 1

Schematic representation of the setting for each condition and timeline of the paradigm. Paradigm outline not to scale. The time allowed for responses ranged from 5 to 15 s, randomly

Fig. 2

Perceived location for back and front stimuli by experimental conditions (actual location and actual distance)

Fig. 3

Distance evaluation for back and front stimuli

Fig. 4

Back–Front location accuracy for Close (50) and Far (100) stimuli

Fig. 5

Distance accuracy ratio for Close (50) and Far (100) stimuli

Fig. 6

Samples of sEMG blink reflex data (a) for Front Close (b) and Far (c) and for Back Close (d) and Far (e) conditions