Error(s) in re-building vignettes:
--- re-building 'adaptation_level.Rmd' using rmarkdown
Loading required package: Rcpp

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Scale for 'x' is already present. Adding another scale for 'x', which will replace the existing scale.
Scale for 'y' is already present. Adding another scale for 'y', which will replace the existing scale.
--- finished re-building 'adaptation_level.Rmd'

--- re-building 'afterimages.Rmd' using rmarkdown
Loading required package: Rcpp

********************************************************
Note: As of version 1.0.0, cowplot does not change the
  default ggplot2 theme anymore. To recover the previous
  behavior, execute:
  theme_set(theme_cowplot())
********************************************************


Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

--- finished re-building 'afterimages.Rmd'

--- re-building 'flanker.Rmd' using rmarkdown
Loading required package: Rcpp

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Warning in y1 - y2 :
  longer object length is not a multiple of shorter object length
Warning in y1 - y2 :
  longer object length is not a multiple of shorter object length
Quitting from lines 200-202 (flanker.Rmd) 
Error: processing vignette 'flanker.Rmd' failed with diagnostics:
result would be too long a vector
--- failed re-building 'flanker.Rmd'

--- re-building 'stroop.Rmd' using rmarkdown
Loading required package: Rcpp
Scale for 'fill' is already present. Adding another scale for 'fill', which will replace the existing scale.
--- finished re-building 'stroop.Rmd'

SUMMARY: processing the following file failed:
  'flanker.Rmd'

Error: Vignette re-building failed.
Execution halted