Notes on Raghubir and Krishna (1999) – Vital Dimensions in Volume Perception

Paper: “Vital Dimensions in Volume Perception: Can the Eye Fool the Stomach?”

Main Topic or Phenomenon

This paper examines how container shape affects consumer volume perceptions and consumption behavior. The central phenomenon is that consumers systematically misjudge the volume of containers based on their elongation (height-to-width ratio), with taller containers perceived as larger even when actual volume is identical.

Theoretical Construct

The paper develops and tests the elongation hypothesis - the idea that consumers use container height as a simplifying visual heuristic for volume judgments. Key constructs include:

• Perceived Volume: Consumer estimates of container capacity before consumption
• Perceived Consumption: Consumer estimates of how much they consumed after drinking/eating
• Perceived Size-Consumption Illusion (PCI): A novel construct showing that volume perceptions reverse before vs. after consumption - taller containers are perceived as larger initially but consumers believe they consumed less from them afterward
• Elongation Effect: The systematic bias where more elongated (taller, narrower) containers are perceived as having greater volume than shorter, wider containers of identical capacity

Key Findings

1. Volume Perception Bias: Taller containers are consistently perceived as larger in volume than shorter containers of identical capacity (Studies 1-2)
2. Consumption Reversal: Despite perceiving taller containers as larger initially, consumers believe they consumed less from taller containers after consumption (Study 3)
3. Increased Actual Consumption: Consumers actually drink more from taller containers (Studies 4-5)
4. Mediation Path: The effect of container shape on actual consumption is mediated by perceived consumption, not perceived volume
5. Preference and Choice: Consumers prefer and choose taller containers (Studies 5-6)
6. Lower Satisfaction: Despite consuming more, consumers report lower satisfaction when drinking from taller containers (Study 7)

Boundary Conditions and Moderators

The paper identifies several important boundary conditions:

• Cognitive Load: The elongation effect persists even under high cognitive load, suggesting it may be partially automatic (Study 2)
• Motivation: High motivation to be accurate does not eliminate the bias
• Package Familiarity: The effect occurs even with familiar package shapes
• Container Material: Material type (glass, plastic, tin, cardboard) can influence volume perceptions
• Volume Size: Some evidence suggests the effect may be stronger for smaller volumes

The authors note that boundary conditions requiring further research include: whether the effect holds when width (rather than height) is more salient, limits of the elongation ratio, and effects of package familiarity over time.

Building on Previous Work

This paper significantly extends prior research in several ways:

From Cognitive Psychology: Builds on Piaget’s work on children’s volume conservation and the “centration hypothesis” (children focus on height when judging volume), extending it to adult consumers in marketplace contexts.

From Size-Weight Illusion Literature: Draws parallels to the well-established size-weight illusion where larger objects feel lighter when they weigh the same, proposing that volume-consumption judgments follow similar expectancy disconfirmation patterns.

From Marketing: Extends Wansink’s research on package size effects on consumption by focusing on perceived (rather than actual) volume differences and introducing shape as a key variable.

Novel Contributions: First to study “perceived consumption” as a construct and first to demonstrate the sequential relationship between perceived volume, perceived consumption, and actual consumption.

Major Theoretical Contribution

The paper makes several significant theoretical contributions:

1. Introduces Perceived Consumption: Develops a new construct examining how much consumers believe they have consumed, distinct from actual consumption
2. Demonstrates the PCI: Shows that perceptions can systematically reverse before vs. after consumption, creating an illusion similar to the size-weight illusion
3. Sequential Processing Model: Establishes that perceived volume → perceived consumption → actual consumption, with perceived consumption (not perceived volume) mediating effects on behavior
4. Expectancy Disconfirmation in Sensory Experience: Extends expectancy disconfirmation theory to sensory consumption experiences rather than just attitudinal domains

Major Managerial Implications

Package Design Strategy: Companies should consider more elongated package shapes to:

• Increase perceived value (packages appear larger)
• Accelerate consumption (consumers drink/eat more)
• Potentially charge premium prices

Positioning Considerations: The effect creates a “double-win” - packages are both more likely to be chosen and consumed faster, though this may reduce post-consumption satisfaction.

Communication Strategy: Companies may need to highlight actual volume differences in advertising since consumers may not naturally notice them.

Pricing Implications: Understanding volume perception biases can inform pricing strategies, particularly for premium positioning.

Unexplored Theoretical Factors

Several potentially important moderators were not examined:

Individual Differences:

• Need for cognition (high-NFC consumers might be less susceptible)
• Visual processing styles or spatial ability
• Cultural differences in spatial perception
• Age-related changes in heuristic use

Contextual Factors:

• Purchase vs. consumption context effects
• Social consumption settings
• Time pressure during decision-making
• Presence of competing products with different shapes

Product Categories:

• Hedonic vs. utilitarian products
• Product involvement levels
• Frequency of category consumption
• Products where “less is more” (e.g., medicine, alcohol)

Sensory Factors:

• How taste, smell, or texture might interact with shape effects
• Temperature effects (hot vs. cold beverages)
• Viscosity or thickness of contents

Psychological Mechanisms:

• The role of attention and eye movement patterns
• Memory effects and learning from repeated exposure
• Individual differences in susceptibility to visual illusions

Reference

Raghubir, Priya and Aradhna Krishna (1999), “Vital Dimensions in Volume Perception: Can the Eye Fool the Stomach?,” Journal of Marketing Research, 36 (3), 313–26.