Asymmetrical Effects of Adaptation to Left- and Right-Shifting Prisms Depends on Pre-existing Attentional Biases

Abstract

Proposals that adaptation with left-shifting prisms induces neglect-like symptoms in normal individuals rely on a dissociation between the post-adaptation performance of individuals trained with left- versus right-shifting prisms (e.g., Colent, et al. 2000). A potential problem with this evidence is that normal young adults have an a priori leftward bias (e.g., Jewell & McCourt, 2000). In Experiment 1, we compared the line bisection performance of young adults to that of aged adults, who as a group may lack a leftward bias in line bisection. Participants trained with both left- and right-shifting prisms. Consistent with our hypothesis, while young adults demonstrated aftereffects for left, but not right prisms, aged adults demonstrated reliable aftereffects for both prisms. In Experiment 2, we recruited a larger sample of young adults, some of whom were right-biased at baseline. We observed an interaction between baseline bias and prism-shift, consistent with the results of Experiment 1: Left-biased individuals showed a reduced aftereffect when training with right-shifting prisms and right-biased individuals showed a reduced aftereffect when training with left-shifting prisms. These results suggest that previous failures to find generalizable aftereffects with right-shifting prisms may be driven by participants’ baseline biases rather than specific effects of the prism itself.

Adult developmental trajectories of pseudoneglect in the tactile, visual and auditory modalities and the influence of starting position and stimulus length

“…The present results for visual bisection are at odds with some published data which has suggested that older adults show reduced pseudoneglect (Fujii et al, 1995;Stam & Bakker, 1990;Benwell et al, 2014b;Schmitz & Peigneux, 2011;Barrett & Craver-Lemley, 2008;Goedert et al, 2010), so it is necessary to consider why this may be. One speculative candidate may be method: Benwell et al (2014b) and Schmitz & Peigneux (2011) both used variants of the 'Landmark' task, in which judgements are made about a pre-bisected presented line: it may be that this task requires more fine grained perceptual evaluation, and thus elicits higher levels of real or perceived difficulty, , and that this causes additional recruitment of areas in the contralateral hemisphere, which is a clear possibility under the CRUNCH model of aging (Reuter-Lorenz and Cappell, 2008) and may also be so under the HAROLD model (Cabeza, 2002;Cabeza, et al, 1997;2002).…”

“…It should be noted that the minimum age of older adult participants in our study is a little younger than in other comparable visual pseudoneglect studies (e.g. Benwell et al, 2014;Goedert et al, 2010;Learmonth et al, 2015;Nagamatsu,et al, 2011;Schmitz & Peigneux, 2011). These younger participants show a greater left-bias.…”

“…There is now additional research to draw upon. Reduced or reversed rightward biases have been reported on visuo-spatial line bisection or landmark tasks (where participants classify pre-bisected line stimuli: Barrett & Craver-Lemley, 2008;Benwell, Thut, Grant & Harvey, 2014b;Schmitz & Peigneux, 2011;Goedert, LeBlanc, Tsai & Barrett, 2010; see also Schmitz, Dehon & Peigneux, 2013). There is also evidence that males and females may produce differential patterns of pseudoneglect over aging, with older females exhibiting more consistent left biases, whilst older males may exhibit a drift into rightward bias with age (Varnava & Halligan, 2007;Chen, Goedert, Murray, Kelly, Ahmeti, Barrett, 2011).…”

“…Another possibility relates to the gender balance in our study (61% female in the older adults), given that Varnava and Halligan (2007) and Chen et al (2011) reported some gender effects on these tasks. However, it is to be noted that both the Varnava and Halligan and also the Failla et al (2003) studies showed some evidence of left bias in older adults, in contrast to, for example, Goedert et al, 2010, Barrett et al (2008 and Chen et al (2011), yet all of these studies utilised groups that approached or attained equality in gender mix despite varying in the extent to which they evidenced line bisection pseudoneglect. Finally, we acknowledge that it is difficult to provide evidence for the absence of any age effect, but our post-hoc power analysis indicates that it is unlikely that we have overlooked medium effects.…”

A rightward shift in the visuospatial attention vector with healthy aging

“…It is possible that a reduction in general alertness/vigilance over the lifespan (Robinson and Kertzman, 1990; Buysse et al, 2005; Nebes et al, 2009; Goedert et al, 2010) may also contribute to the chronic attenuation of pseudoneglect in the elderly.…”