The study explores how people recognize objects despite differences in their retinal projections when viewed at different orientations. It examines the role of mental rotation and orientation dependence in shape recognition. The authors propose that shapes are represented in memory as structural descriptions in object-centered coordinate systems, allowing for recognition regardless of orientation. However, alternative hypotheses suggest that shapes are represented in a single canonical orientation, with mental rotation transforming input shapes to that orientation before comparison. Another hypothesis posits that shapes are stored in multiple representations, each corresponding to a different orientation. In four experiments, subjects studied several objects at a single orientation and were tested at various orientations. Initially, response times increased with orientation departure, suggesting mental rotation. With practice, response times stabilized across orientations, indicating stored representations. When tested at novel orientations, response times increased with orientation disparity, suggesting stored representations were used to recognize new orientations through rotation. The results support a hybrid model combining mental transformation and multiple view hypotheses. Input shapes are transformed to a stored view, either the nearest or canonical orientation. Interestingly, when mirror images were presented, response times were consistent across orientations, suggesting mental rotation aligns input shapes with stored counterparts. The study also addresses the role of mental rotation in handedness judgments. While mental rotation is used to determine handedness, it is not necessarily used for shape recognition. However, the results suggest that mental rotation is used for recognizing unfamiliar shapes, with practice reducing orientation effects. The study highlights the complexity of shape recognition, involving multiple mechanisms. It shows that orientation effects on recognition time depend on familiarity and the type of task. The findings suggest that mental rotation plays a role in recognizing unfamiliar shapes, while orientation-invariant representations are used for familiar ones. The results also indicate that practice can reduce orientation effects, either by developing orientation-invariant representations or by storing multiple orientation-specific representations. The study concludes that the role of mental rotation in shape recognition is not fully understood, and further research is needed to clarify the mechanisms involved.The study explores how people recognize objects despite differences in their retinal projections when viewed at different orientations. It examines the role of mental rotation and orientation dependence in shape recognition. The authors propose that shapes are represented in memory as structural descriptions in object-centered coordinate systems, allowing for recognition regardless of orientation. However, alternative hypotheses suggest that shapes are represented in a single canonical orientation, with mental rotation transforming input shapes to that orientation before comparison. Another hypothesis posits that shapes are stored in multiple representations, each corresponding to a different orientation. In four experiments, subjects studied several objects at a single orientation and were tested at various orientations. Initially, response times increased with orientation departure, suggesting mental rotation. With practice, response times stabilized across orientations, indicating stored representations. When tested at novel orientations, response times increased with orientation disparity, suggesting stored representations were used to recognize new orientations through rotation. The results support a hybrid model combining mental transformation and multiple view hypotheses. Input shapes are transformed to a stored view, either the nearest or canonical orientation. Interestingly, when mirror images were presented, response times were consistent across orientations, suggesting mental rotation aligns input shapes with stored counterparts. The study also addresses the role of mental rotation in handedness judgments. While mental rotation is used to determine handedness, it is not necessarily used for shape recognition. However, the results suggest that mental rotation is used for recognizing unfamiliar shapes, with practice reducing orientation effects. The study highlights the complexity of shape recognition, involving multiple mechanisms. It shows that orientation effects on recognition time depend on familiarity and the type of task. The findings suggest that mental rotation plays a role in recognizing unfamiliar shapes, while orientation-invariant representations are used for familiar ones. The results also indicate that practice can reduce orientation effects, either by developing orientation-invariant representations or by storing multiple orientation-specific representations. The study concludes that the role of mental rotation in shape recognition is not fully understood, and further research is needed to clarify the mechanisms involved.