Selecting appropriate designs and comparison conditions in repetition paradigms

doi:10.1016/j.cortex.2015.10.022

Cortex

Volume 80, July 2016, Pages 196-205

https://doi.org/10.1016/j.cortex.2015.10.022 Get rights and content

Abstract

The studies described by Vogels (this issue) demonstrate the complexity of repetition effects in the visual processing stream. In addition to signal suppression, findings of inherited effects from earlier processing, and discrepancies between the stimulus selectivity of cells before and after repetition, have informed the inferences that can be drawn from measures over larger scales such as functional magnetic resonance imaging (fMRI) or electroencephalography (EEG). This work also demonstrates that integration of evidence across recording methods is vital for understanding repetition effects in the brain. It is however difficult to integrate evidence across different recording methods and repetition paradigms. At the crux of this difficulty is the selection of comparison or unrepeated stimulus conditions within paradigms, which influence the observed strength, selectivity and even direction of repetition effects. This viewpoint highlights prevalent methodological issues with regard to repeated-unrepeated stimulus comparisons: inherited adaptation, stimulus specific expectations, concurrent memory retrieval, stimulus novelty and familiarity, attention, and changes in neuronal selectivity with repetition. The extent to which current conflicting and uncertain findings are due to selection of unrepeated stimulus conditions is unknown, but needs to be addressed to develop models of repetition spanning recording methods and repetition paradigms.

Introduction

Repetition of a stimulus leads to prior exposure-dependent changes in response properties of cortical neurons, widely known as repetition suppression (Desimone, 1996, Ringo, 1996) or adaptation (Kohn, 2007). Repetition suppression is defined as a stimulus-specific reduction in neuronal activity (e.g., neuronal firing rate, functional magnetic resonance imaging (fMRI) blood-oxygen-level dependent (BOLD) signal or scalp-recorded potential) to repeated compared to unrepeated stimuli (Grill-Spector, Henson, & Martin, 2006; depicted in Fig. 1a). In a small number of cases stimulus repetition can also lead to an increase in a measure of neuronal activity, termed repetition enhancement (Henson et al., 2000, James et al., 2000, Segaert et al., 2013). Adaptation occurs with stimulus repetition but indexes a more diverse array of effects than repetition suppression, including changes in response magnitude and the shape and width of tuning curves to stimulus features (Kohn, 2007, Wissig and Kohn, 2012). These adaptation effects can vary over the time course of a neuron's response, and the time window of analysis can be crucial to delineate adaptation effects in the initial part of the response (e.g., Kaliukhovich and Vogels, 2012, Liu et al., 2009) from later effects of adaptation on intracortical interactions (Patterson, Wissig, & Kohn, 2013) or prediction-related suppression of neuronal activity (Grotheer and Kovács, 2015, Summerfield et al., 2011, Todorovic and de Lange, 2012).

The studies summarized in Vogels (2016) have greatly influenced our understanding of the complex array of repetition effects in the visual system. Several key experiments (De Baene and Vogels, 2010, Sawamura et al., 2006) have found not only increases or decreases in neuronal activity with repetition, but also inherited effects from earlier visual processing and changes in the stimulus-selectivity of neurons. These results have provided valuable information about the inferences that can be drawn from repetition effects observed using fMRI BOLD or electroencephalography (EEG)/magnetoencephalography (MEG). They also demonstrate that careful integration of evidence across recording methods is necessary to understand repetition effects, given the differential sensitivity of each recording method to different aspects of neuronal activity (Logothetis, 2008). In this sense, each recording method provides a “piece of the puzzle”, in which suppression in one measure may even co-occur with enhancement in another (De Baene and Vogels, 2010, Stopfer and Laurent, 1999).

These studies also remind us that repetition-induced suppression or enhancement is a change measure and therefore inherently relies on a comparison condition: the response to an equivalent unrepeated stimulus. The unrepeated stimulus condition dictates the detection of repetition-specific suppression/enhancement separate from other phenomena such as changes in attention and expectation (Kovács & Vogels, 2014). A significant challenge in harmonizing evidence across studies and measures of neuronal activity stems from the different paradigms, featuring different unrepeated stimulus conditions, which are used to define repetition effects. The choice of unrepeated stimulus condition guides the interpretability, strength, specificity and possibly even direction of the effect.

This viewpoint focuses on factors relevant to repeated-unrepeated stimulus comparisons in adaptation and repetition paradigms. Firstly, general issues relating to repeated-unrepeated stimulus comparisons in repetition paradigms are identified. Following this, the basic versions of major paradigms in the field are evaluated according to advantages and disadvantages of the unrepeated stimulus condition choice. This viewpoint concludes with a discussion of how confounding factors differ across paradigms, and ways to investigate the influences of confounding factors on existing reports of repetition-specific effects.

Section snippets

Inherited adaptation from earlier stages

Repetition effects occur in multiple levels of the visual system, and there is strong evidence of changes in high-level visual areas as a result of altered input from upstream regions such as early visual cortex (Kohn and Movshon, 2003, Larsson and Harrison, 2015, Solomon et al., 2004, Tolias et al., 2005). Isolating high-level repetition effects is especially difficult because repeated stimuli typically share low-level visual features such as local orientation or curvature information, in

Within-trial repetition designs

Within-trial repetition designs present trials of two consecutive stimuli (adapter and test) separated by an interstimulus interval, displayed in Fig. 1. These designs allow event-related fMRI analyses to estimate the time-course of the BOLD response, at the cost of decreased detection power compared to blocked designs (Liu, Frank, Wong, & Buxton, 2001). In these cases it is important to balance the trial order across conditions, for example using M-sequences (Buračas & Boynton, 2002).

Integrating evidence across paradigms

From the evaluation of the above paradigms it appears that there is no optimal repeated-unrepeated stimulus comparison for all purposes. Within-trial, blocked and oddball designs can be affected by inherited adaptation effects and imbalances in stimulus-specific expectations between the repeated and unrepeated stimuli, both of which may have contributed to observed repetition effects in many previous experiments. Across-trial and delayed match-to-sample designs provide some control over these

Conclusions

The issues related to repeated-unrepeated stimulus comparisons described in this viewpoint can affect the magnitude, detectability, stimulus-selectivity and even direction of observed repetition effects. In order to develop quantitative models of repetition effects across recording methods, these unrepeated stimulus-related confounds should be further investigated to estimate the magnitude of their effects and specificity to different measures of neuronal activity. Existing designs (Grotheer

Acknowledgements

D.F. thanks Hannah A.D. Keage for her insightful commentary on earlier drafts, and Alina Peter, whose discussions with the author formed the basis of this paper.

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Special issue: ViewpointSelecting appropriate designs and comparison conditions in repetition paradigms

Abstract

Introduction

Section snippets

Inherited adaptation from earlier stages

Within-trial repetition designs

Integrating evidence across paradigms

Conclusions

Acknowledgements

Neuron

Trends in Neurosciences

NeuroImage

NeuroImage

NeuroImage

Neuron

Neuron

Neuron

Neuropsychologia

Neuropsychologia

Vision Research

Progress in Neurobiology

Trends in Cognitive Science

NeuroImage

Neuropsychologia

Neuron

Current Biology

Neuron

Neuropsychologia

NeuroImage

NeuroImage

Trends in Neurosciences

NeuroImage

Neuron

Behavioural Brain Research

Neuron

Neuropsychologia

Neuron

Vision Research

Cortex

Neuropharmacology

Stimulus predictability reduces responses in primary visual cortex

Journal of Neuroscience

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Experimental Brain Research

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Visual Neuroscience

Fitting the mind to the world: Adaptation and after-effects in high-level vision

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Science

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Cerebral Cortex

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Proceedings of the National Academy of Sciences of the United States of America

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Nature

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BMC Neuroscience

Expectation and surprise determine neural population responses in the ventral visual stream

Journal of Neuroscience

Two kinds of FMRI repetition suppression? Evidence for dissociable neural mechanisms

Journal of Neurophysiology

Neuronal activity related to visual recognition memory: long-term memory and the encoding of recency and familiarity information in the primate anterior and medial inferior temporal and rhinal cortex

Experimental Brain Research

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Cerebral Cortex

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Journal of Neurophysiology

Stimulus-specific adaptation in auditory cortex is an NMDA-independent process distinct from the sensory novelty encoded by the mismatch negativity

Journal of Neuroscience

Searching for the mismatch negativity in primary auditory cortex of the awake monkey: deviance detection or stimulus specific adaptation?

Journal of Neuroscience

A theory of cortical responses

Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences

Special issue: Viewpoint
Selecting appropriate designs and comparison conditions in repetition paradigms