The Robins conceded from two corners in the opening 19 minutes of the game, which left Pearson ruing the inconsistency in his side.
Following the game, Pearson spoke about The Robins' inconsistency, conceding from set pieces, Bristol City's away form, injuries sustained in the game and the travelling fans.
On Bristol City's inconsistent performances
"Unfortunately we just don't perform well enough at times, we've put in a performance which doesn't match our previous one.
"It's about players being able to reproduce performances, but the big problem for us is as a collective we still struggle to find that elusive consistency of performance."
In contrast, it was another poor result for Pearson and his players, who were sluggish and struggled to really produce any kind of threat in the game.
There were chances for the visitors but they were few and far between, and crucially not taken, leaving a lot to be desired from the former Premier League manager's point of view.
Going into the game, The Robins had the opportunity to secure consecutive wins for the first time in their season and up against relegation strugglers Barnsley, Pearson must have believed this was the chance to end that record.
It was not to be however, and the fact that The Tykes had plenty of openings to score more than just the two will also be a concern to Pearson, who had seen his side keep a clean sheet at Blackburn Rovers just a few days earlier.
On The Robins' failure to defend set pieces
"Tonight we conceded two really poor goals from a lack of concentration and application.
"That's where we continue to cause our own problems."
The issue of defending set pieces cropped up again for Bristol City and Amine Bassi was able to expose just how poor The Robins are in terms of their efforts to keep corners out.
The Moroccan midfielder put in two corners in the opening 19 minutes of the game, both of them leading to goals.
The first saw the cross go through the entirety of the box before Matty Wolfe flicked the ball on to Morris to score, highlighting the inability of Bristol City's defence to clear the danger.
Conceding another just ten minutes later through Helik did not help to allay any fears about Bristol City's ability to defend set pieces.
With The Robins already having a shaky defensive record on the road, having their inability to defend corners exposed so easily by Barnsley will be likely to work against Pearson's side as teams continue to target Bristol City's weak aerial ability.
On Bristol City's away form
"When you compare how we were today and how solid we were on Saturday, it's too big a difference.”
The Robins' boss said that it is all too often that his side take one step forwards just to take another backwards.
Bristol City's display on the night compared to their 0-1 away win against Blackburn Rovers on Saturday is the perfect example of that.
Saturday's game saw the Bristol City's away supporters enjoy their first win on the road in five months, including a first clean sheet on their travels in 23 games.
Despite this, The Robins could only produce a tame showing against relegation threatened Barnsley, missing the opportunity to move further away from the relegation zone and build on the previous away win.
The result and particularly the performance which accompanied it was clearly frustrating for Pearson, who saw his game plan unravel in 19 minutes on Tuesday evening.
The attempt to change the tactics and provide a different kind of threat did not make much of a difference to the complexion of the tie either.
On the injuries to Alex Scott and Joe Williams
"Alex [Alex Scott] has got a bit of an ankle problem we don't know how that will be until tomorrow.
"Likewise with Joe [Joe Williams], he's got a tight hamstring so we'll have to see how that is."
Pearson said that the damage was already done by the time he lost the pair to injury, however the 58-year-old will be concerned by the prospect of having to lose both Scott and Williams to injury.
Scott has made 32 appearances for Bristol City so far this season, and losing the 18-year-old to injury will not have been in Pearson's plans, as he looks to develop their academy prospect.
To have featured as often as he has at such a young age, it is clear that Pearson believes the English midfielder has the quality required to play at Championship level, and so he will miss the youngster should he be out for an extended period.
Williams had also just picked up a knock which was the reason why he did not start the game on Tuesday night, so Pearson will hope that Williams has not suffered any further damage to his hamstring.
Pearson also lamented the fact that his squad picked up two injuries, having been pleased with the fitness in the squad going into the game.
He did, however, accept that dealing with such absences is part of his job as manager of The Robins.
On the travelling fans
"As I came off [the pitch] there were some fans letting me know what they thought and I can't disagree with them.
"They follow us in big numbers and they spend a lot of money in supporting us and we should give them a better performance than that in all honesty."
It is no real secret that the away games have not brought much joy for the travelling fans in recent months.
Pearson's acknowledgement of the supporters' frustrations was understandable given the fact that The Robins have gone from winning four of their first five on the road this term to not getting an away win from the October 2 until last Saturday.
The 2-3 win against Peterborough United back in October feels a long time ago now, and with only one of 13 of their last away games producing a win, it is clear that Pearson's side would benefit from picking up more points away from home.