The visual representations of motion and of gravity are functionally independent: Evidence of a differential effect of smooth pursuit eye movements

Abstract

The memory for the final position of a moving object which suddenly disappears has been found to be displaced forward, in the direction of motion, and downwards, in the direction of gravity. These phenomena were coined, respectively, Representational Momentum and Representational Gravity. Although both these and similar effects have been systematically linked with the functioning of internal representations of physical variables (e.g. momentum and gravity), serious doubts have been raised for a cognitively based interpretation, favouring instead a major role of oculomotor and perceptual factors which, more often than not, were left uncontrolled and even ignored. The present work aims to determine the degree to which Representational Momentum and Representational Gravity are epiphenomenal to smooth pursuit eye movements. Observers were required to indicate the offset locations of targets moving along systematically varied directions after a variable imposed retention interval. Each participant completed the task twice, varying the eye movements' instructions: gaze was either constrained or left free to track the targets. A Fourier decomposition analysis of the localization responses was used to disentangle both phenomena. The results show unambiguously that constraining eye movements significantly eliminates the harmonic components which index Representational Momentum, but have no effect on Representational Gravity or its time course. The found outcomes offer promising prospects for the study of the visual representation of gravity and its neurological substrates.

Implied tactile motion: Localizing dynamic stimulations on the skin

“…Hence, if a stimulus moves, it would be reasonable for the sensory system to predict the next sensory input in the direction of anticipated motion. In line with such a suggestion, Berry and colleagues (1999) found an anticipation effect for visual stimuli moving across the retina (see De sá Teixeira, 2016;Hubbard, 2005Hubbard, , 2014Kerzel, 2000, for discussion concerni ng the i nfl uence of eye m ovements on representational momentum). Interestingly, most theories of representational momentum consider this effect to be modality-independent (see Hubbard, 2010).…”

“…In the horizontal plane, most studies have not reported any difference between left-and rightward movement (Cooper & Munger, 1993;Hubbard, 1990Hubbard, , 1995aHubbard & Bharucha, 1988; but see Halpern & Kelly, 1993). In the vertical plane, downward movement/ descending stimuli tend to elicit stronger forward shifts than upward m ovement/ascending stimul i, known as representational gravity (e.g., De sá Teixeira, 2016;De sá Teixeira, Hecht, & Oliveira, 2013;Hubbard, 1990Hubbard, , 1995bHubbard, , 2005. For stimuli that move in the depth plane, a forward shift has been evidenced, yet consistent differences between approaching and receding events have not been reported.…”

Vestibular Stimulation Interferes with the Dynamics of An Internal Representation of Gravity

“…Importantly enough, and although eye movements were found to follow a course similar to the behavioural findings when left unconstrained (Experiment 2), the pattern of spatial mislocalization did not change when observers were forced to keep their gaze steady (Experiments 3a and 3b). These results have been interpreted as resulting from an internal model of gravity that modulates the spatial updating in memory of the remembered vanishing location (De Sá Teixeira, 2016b;De Sá Teixeira & Oliveira, 2014).…”

“…To start with, one should notice that any spatial localization error of a moving target is determined by two independent phenomena (see De Sá Teixeira, 2014, 2016bDe Sá Teixeira & Hecht, 2014;Motes, Hubbard, Courtney, & Rypma, 2008), each linked with its own reference direction. On the one hand, representational momentum, predicting an error forward, should depend solely on the target's motion direction.…”

Gravity prior in human behaviour: a perceptual or semantic phenomenon?

“…Since the beginning of time, all living organisms have evolved under a constant terrestrial gravitational field of approximately 9.81 m/s 2 , known as 1 g. On Earth, gravity is always there; it is therefore not surprising that the physical constraints of Earth’s gravity are internalised in the human brain to shape our perception and action (Indovina et al 2005 ). For instance, random accelerations are hardly perceived at all (Werkhoven et al 1992 ), falling objects are expected to accelerate even when their velocity is constant (Zago et al 2004 ), and observers misremember the location of moving objects in space (De Sá Teixeira 2016 ). In addition, gravity can influence eye movements, with improved smooth pursuit of objects which move according to 1 g vs objects which move according to weightlessness (0 g), reversed gravity (− 1 g), or hypergravity (2 g) (Delle Monache et al 2015 ; Jörges and López-Moliner 2019 ).…”