Visual asymmetries between ON and OFF pathways.

Vision's Hidden Pathways: How ON and OFF Signals Shape What You See

Author's portrait.
Lena Kashyap in Science & Nature August 2025 • 4 min read.

"Uncover the surprising differences in how your brain processes light and dark, and what it means for visual perception."


Our perception of the world relies on a sophisticated system of visual processing, largely organized into what are known as ON and OFF pathways. These pathways act as specialized channels, with ON pathways signaling increases in light (stimulus increments) and OFF pathways responding to decreases in light (stimulus decrements). This division allows us to perceive both bright and dark elements in our environment, creating a balanced visual experience.

These ON and OFF pathways aren't just mirror images of each other; they exhibit natural pairings based on morphological and physiological similarities. A classic example is the ON and OFF alpha ganglion cells found in mammalian retinas. However, the nuances of these pathways reveal that they function differently, a phenomenon known as asymmetry.

Imagine that the ON and OFF pathways are like two different types of paint brushes. ON pathways highlight aspects of an image while OFF pathways do the opposite, and scientists have noted that the properties of ON and OFF pathways are not always equal. For example, research has shown that spatial receptive fields of OFF alpha cells—the specific areas of the visual field that these cells respond to—are systematically smaller than those of their ON counterparts. But how consistent are these asymmetries across different types of retinal cells?

Decoding the ON/OFF Asymmetry: What Does It All Mean?

Visual asymmetries between ON and OFF pathways.

To explore the consistency of ON/OFF asymmetries, researchers delved into the spatiotemporal receptive field (RF) properties of multiple retinal ganglion cell (RGC) types in rat retinas. By employing quantitative and serial classification methods, they identified three functional pairs of ON and OFF RGCs. These pairs became the focal point for analyzing the structure of their RFs and comparing spatial integration, temporal integration, and gain—critical aspects of visual processing.

Interestingly, the study found that RGC types with larger spatial RFs exhibited briefer temporal integration and higher gain, aligning with results from studies on cats and primates. However, when examining individual ON and OFF RGC pairs, the researchers uncovered a more complex picture: each pair displayed distinct asymmetric relationships in receptive field properties, some of which contradicted previous findings. For instance, some pairs showed an opposite pattern to what had been previously reported. What are the implications of these findings?

  • Spatial Receptive Fields: Discovered the size differences between ON and OFF cell receptive fields varied among different cell types.
  • Temporal Integration: Revealed how quickly cells respond to changes in light, showing different patterns of integration between ON and OFF cells.
  • Gain Control: Demonstrated how sensitive cells are to changes in contrast, which influences how we perceive brightness and darkness.
These results underscore the intricate functional organization of six RGC types in the rodent retina and indicate that ON/OFF asymmetries are pathway-specific. This means that the functional organization of vision across diverse ON and OFF signaling pathways are far more nuanced than previously thought.

Why This Matters: Implications for Vision and Beyond

Understanding the specific asymmetries in ON and OFF pathways is pivotal for deciphering how our brains process sensory information. The study highlights that visual processing is not uniform; instead, it is a mosaic of specialized functions that fine-tune our perception. By revealing the unique characteristics of different ON/OFF pairs, this research paves the way for new insights into visual disorders and potential therapeutic interventions. Additionally, understanding the functional diversity of retinal ganglion cells can inspire advancements in artificial vision and neuromorphic computing.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

1

What are ON and OFF pathways and how do they contribute to our visual experience?

ON and OFF pathways are specialized channels in the visual system. ON pathways signal increases in light (stimulus increments), while OFF pathways respond to decreases in light (stimulus decrements). They work in tandem, allowing us to perceive both bright and dark elements, resulting in a balanced visual experience. The functional organization of vision across diverse ON and OFF signaling pathways are far more nuanced than previously thought.

2

How do ON and OFF pathways differ, and what does asymmetry mean in the context of visual processing?

ON and OFF pathways are not identical; they display asymmetries. Asymmetry refers to the functional differences between ON and OFF pathways. For example, research has shown that spatial receptive fields of OFF alpha cells are systematically smaller than those of their ON counterparts. This means that the specific areas of the visual field that these cells respond to differ between ON and OFF cells. These differences are pathway-specific.

3

Can you explain the role of spatial receptive fields, temporal integration, and gain control in ON and OFF pathways?

These are critical aspects of visual processing. Spatial receptive fields determine the area of the visual field that cells respond to. Temporal integration refers to how quickly cells respond to changes in light, with different patterns observed between ON and OFF cells. Gain control indicates how sensitive cells are to changes in contrast, influencing how we perceive brightness and darkness. The study found that RGC types with larger spatial RFs exhibited briefer temporal integration and higher gain.

4

What were the key findings regarding the asymmetries of ON and OFF pathways in the rodent retina?

The study revealed pathway-specific asymmetries. Researchers identified three functional pairs of ON and OFF retinal ganglion cells (RGCs) and analyzed their receptive field properties. They found that each pair displayed distinct asymmetric relationships in receptive field properties. Some pairs showed an opposite pattern to what had been previously reported. The size differences between ON and OFF cell receptive fields varied among different cell types. Also, different patterns of integration between ON and OFF cells, and the sensitivity of the cells to changes in contrast were demonstrated.

5

Why is understanding the asymmetries in ON and OFF pathways important, and what are the potential implications?

Understanding these asymmetries is pivotal for deciphering how brains process sensory information. The research highlights that visual processing is not uniform but a mosaic of specialized functions that fine-tune our perception. By revealing the unique characteristics of different ON/OFF pairs, this research paves the way for new insights into visual disorders and potential therapeutic interventions. Additionally, understanding the functional diversity of retinal ganglion cells can inspire advancements in artificial vision and neuromorphic computing.

Newsletter Subscribe

Subscribe to get the latest articles and insights directly in your inbox.