Lack of evidence for associative learning in pea plants

Abstract

Gagliano et al. (Learning by association in plants, 2016) reported associative learning in pea plants. Associative learning has long been considered a behavior performed only by animals, making this claim particularly newsworthy and interesting. In the experiment, plants were trained in Y-shaped mazes for 3 days with fans and lights attached at the top of the maze. Training consisted of wind consistently preceding light from either the same or the opposite arm of the maze. When plant growth forced a decision between the two arms of the maze, fans alone were able to influence growth direction, whereas the growth direction of untrained plants was not affected by fans. However, a replication of their protocol failed to demonstrate the same result, calling for further verification and study before mainstream acceptance of this paradigm-shifting phenomenon. This replication attempt used a larger sample size and fully blinded analysis.Markel. eLife 2020;9:e57614.

Comment on 'Lack of evidence for associative learning in pea plants'

“…In our study ( Gagliano et al, 2016 ) we used blue light as the US which caused consistently a growth of the plant in the direction of the last presentation of the light (100% phototropic response). This was not the case in the study by Markel, where only a slight bias towards the last presentation of light was obtained ( Markel, 2020 ). Since light was not an effective US in the study by Markel, it is not surprising that no distinct associative learning was observed.…”

“…This was necessary to ensure that a plant inside its maze could only receive the blue light we directionally delivered within each maze at set specific times, and was completely shielded from light sources elsewhere. The lack of darkness in the study by Markel (see Figure 1—figure supplement 1C in Markel, 2020 ) is a major departure from our original design. We surmise that by inadvertently allowing individual plants to be exposed to light arriving from multiple sources within a 1.5 m 2 growth cabinet (e.g.…”

“…We offer the following potential explanation for the lack of a consistent phototropism in Markel, 2020 . Our study was conducted inside a completely dark 5.3 m 2 room, where individual Y-mazes were positioned at ample distance (~20 cm radius) from each other.…”

Response to comment on 'Lack of evidence for associative learning in pea plants'

“…The primary criticism of my replication attempt ( Markel, 2020 ) is that light was not shown to be a reliable unconditioned stimulus ( Gagliano et al, 2020 ). It is true that the plants in Markel, 2020 did not always grow towards the last presentation of light, which reduced the power to detect associative learning.…”

“…The primary criticism of my replication attempt ( Markel, 2020 ) is that light was not shown to be a reliable unconditioned stimulus ( Gagliano et al, 2020 ). It is true that the plants in Markel, 2020 did not always grow towards the last presentation of light, which reduced the power to detect associative learning. However, Gagliano et al, 2016 does not emphasize how surprising it is that plants would always grow towards a one hour presentation of light preceded by presentations in the opposite direction.…”