Sensitivity and bias under conditions of equal and unequal academic task difficulty.

Kids picked between two math stations. Each station paid points on the same VI schedule.

First, problems were equally hard. Later, one station got harder while rewards stayed equal.

Researchers tracked how often each child switched to see if difficulty alone could bias choice.

When tasks were equally hard, kids’ time matched the payoff almost perfectly.

Once one station got harder, kids fled to the easier side even though rewards never changed.

Task difficulty acted like a magnet, pulling choice away from strict matching.

Martens et al. (2016) later saw the same matching law in preschool circle time. They proved the rule still holds outside the lab, while D et al. showed an important classroom exception.

McLean et al. (1983) measured sensitivity and bias in pigeons decades earlier. Their bird data gave the exact math tools needed to spot the difficulty bias in kids.

Krägeloh et al. (2003) found that adding signals or change-over delays also twists sensitivity. Together these papers warn: anything that makes one side “feel different” can override the pay sheet.

For BCBAs running academic centers, equal token pay does not guarantee equal staying power. Check the work itself: if one task is tougher, students may avoid it no matter the purse. Balance difficulty across stations or add extra help so reinforcement, not effort level, drives choice.