- Gibson & Walk: Alternative Evidence.
- Camps et al: Infants heart rate changes. Suggests that infants are able to detect a difference in depth. Supports G&W conclusion that some d.p is innate and develops before infants are able to move independently, also possible that d.p is learned in the first few months as increased heart rate indicates this.
- Bower et al: Infants as young as 6 days old were more upset by a smaller object that approached them than the larger object even though the retinal image appeared the same. Also supports the Nativist view that m.p is innate.
- Witherington et al: Infants who had begun to walk were more wary of the visual cliff than infants who were still crawling. Suggests that new learning is gained from a different perspective. Doesn't entirely contradict G&W but does suggest learning is also important in d.p.
- Hock: Claimed that d.p is present at birth, but fear of falling is learned through experience.