Broaching this subject with the mother or carer.

This is always difficult as one's view is interpreted as an admonition and a state of tension is quickly generated. I think the substance of the 2008 study ignores common sense. It is easy to comprehend that bewilderment more that excitement, fear more than pleasure, isolation more than companionship and security, desertion more than love and reassurance figure strongly in the psyche of infants facing forward.
From their first breathe after parturition infants start to learn and from that moment for many years they need reassurance that their environment is safe. The only way that this can happen smoothly is that as each new exposure, incident, visual, auditory, olfactory, taste and touch stimulus is encountered  the infant is assured of it harmlessness or otherwise. This way it learns without distress.

ADULTS SUFFER ANXIETY WHEN EXPOSED TO UNUSUAL ENVIRONMENTS WHEN THEIR IS NO ONE TO ASSURE THEM OF THEIR SAFETY - THIS IS UN-REFUTABLE

THEREFORE HOW MUCH MORE WILL THE INFANT SUFFER - THAT THEY WILL INDEED SUFFER IS COMMON SENSE.

In the aforementioned study heart beat, sleepiness are brought up to qualify anxiety and stress. It admitted that neither were very helpful.

WHAT I WOULD ASK A CARER OR PARENT TO DO IS TO USE COMMON SENSE - YOU CANNOT ASSESS WHAT A STRANGE ENVIRONMENT IS DOING THE INFANT'S BRAIN -

WE ARE NOT SO ADVANCED YET, BUT INTUITIVELY AND OBSERVATIONALLY INFANTS, WHICH MAY BE ONLY DAYS, WEEKS, MONTHS FROM EMERGING FROM THEIR MOTHER'S BELLIES, THAT HAVE THE CONSTANT REASSURANCE ABOUT THE NEWNESS AND PRESENCE OF WHAT THEY ARE CONFRONTED WITH WILL HAVE LOCKED INTO THEIR HEADS MUCH MORE VALID INFORMATION THAN THOSE INFANTS WHO FACING FORWARD, AND AS SUCH DEPRIVED OF THIS REASSURANCE, WILL HAVE TO GUESS WHETHER IT IS GOOD OR BAD -  HAVING TO GUESS WHETHER IT IS GOOD OR BAD ! - ARE  YOU KIDDING -  HOW CAN THEY DO THAT - WHAT IS THEIR REFERENCE POINT - THEY SIMPLY DO NOT KNOW AND WILL ONLY LEARN IN A SECOND HAND MATTER IF AT ALL, WHEN THE INITIAL ALARM, CONFUSION AND  ANXIETY  HAS , HOPEFULLY, GONE AND THAT, SOMEHOW, THEY CAN THEN CORRELATE THAT THEY ARE UNHARMED FROM IT - OF COURSE THEY MAY NEVER BE ABLE TO DO THAT BECAUSE THERE MAY NOT BE TIME BEFORE THE NEXT STRESSFUL STIMULUS AND IN ANY CASE THEIR INHERENT INTELLECTUALITY MAY NOT BE UP TO IT.
SUCH A FAILURE IS REGISTERED IN THE MAP OF THE BRAIN AS NEGATIVE LEARNING
LEARNING BY BITTER EXPERIENCE RATHER THAN LEARNING THROUGH 'ADVICE' AND 'REASSURANCE'.

I have spent years just watching kids and their parents or their guardians in both buggy or pram situations and hands down I see more stress in child facing forward, or its a child with something in its mouth to shut it up or one struggling to turn its head to see its mum than where the child is face to face.
When Sir Muir Gray adds 'Dont worry about the buggy', this is from the common sense point of view I have tried to demonstrate, utter folly.