Perceptual Learning beyond Perception: Mnemonic Representation in Early Visual Cortex and Intraparietal Sulcus

Abstract

The ability to discriminate between stimuli relies on a chain of neural operations associated with perception, memory and decision-making. Accumulating studies show learning-dependent plasticity in perception or decision-making, yet whether perceptual learning modifies mnemonic processing remains unclear. Here, we trained human participants of both sexes in an orientation discrimination task, while using functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) to separately examine training-induced changes in working memory (WM) representation. fMRI decoding revealed orientation-specific neural patterns during the delay period in primary visual cortex (V1) before, but not after, training, whereas neurodisruption of V1 during the delay period led to behavioral deficits in both phases. In contrast, both fMRI decoding and disruptive effect of TMS showed that intraparietal sulcus (IPS) represented WM content after, but not before, training. These results suggest that training does not affect the necessity of sensory area in representing WM information, consistent with the sensory recruitment hypothesis in WM, but likely alters the coding format of the stored stimulus in this region. On the other hand, training can render WM content to be maintained in higher-order parietal areas, complementing sensory area to support more robust maintenance of information.

Sensory Recruitment in Visual Short-Term Memory: A Systematic Review and Meta-Analysis of Sensory Visual Cortex Interference Using Transcranial Magnetic Stimulation

“…A recent study by Jia et al (2021), studying the effects of perceptual training in VSTM, provided strong evidence in support of the sensory recruitment hypothesis for area V1. Specifically, they used an orientation change detection task, where participants had to remember the orientation of one grating presented for 200 ms, and report whether a probe presented after a 4 s delay period had a clockwise or counterclockwise tilt compared to the remember stimulus.…”

“…TMS interference during maintenance. TMS was delivered during the maintenance phase of a VSTM task (i.e., more than 200 ms after stimulus onset) in 14 experiments from twelve different studies (Cattaneo et al, 2012;Jia et al, 2021;Malik et al, 2015;Rademaker et al, 2017;Saad, & Silvanto, 2013;Saad et al, 2015;Silvanto & Cattaneo, 2010;van de Ven et al, 2012;van Lamsweerde, & Johnson, 2017;Zokaei et al, 2014). As discussed in detail below, although the majority of these studies provide evidence supporting the sensory recruitment hypothesis, others either failed to find such evidence or their findings are more consistent with an interaction between perceptual and VSTM processes, as we suggest below.…”

“…Another issue reflected in the results of the included studies, concerns the fact that some studies provided evidence of inhibitory TMS effects (Jia et al, 2021;Rademaker et al, 2017;Silvanto & Cattaneo, 2010;van de Ven et al, 2012;van Lamsweerde, & Johnson, 2017), while others reported facilitatory TMS effects (Cattaneo et al, 2012;Saad et al, 2015; Zokaei e al., 2014) on VSTM performance. Examining the methodological differences between these studies, a possible explanation of this contradiction could lay in the distinct stimulation power output used for TMS.…”

“…Therefore, if this is reflected in the sensory visual cortex's activity, it is possible that enough resources were still available in the sensory visual cortex due to low load VSTM task demands, thus, TMS noise leaves the maintained representations unaffected (see de Graaf, & Sack, 2011). It could be argued that in some cases, where only one stimulus was presented, a strong TMS effect was found (Jia et al, 2021). However, some methodological differences could explain why Jia et al (2021) were able to show an effect despite the sensory load.…”

“…It could be argued that in some cases, where only one stimulus was presented, a strong TMS effect was found (Jia et al, 2021). However, some methodological differences could explain why Jia et al (2021) were able to show an effect despite the sensory load. Specifically, in the Jia et al (2021) study, an orientation stimulus combined with retinotopic mapping was employed, which allowed researchers to identify and stimulate specific V1 areas which correspond closely to the neurons processing the stimulus orientation.…”