Google designers are under a mandate to make the products' interfaces more appealing, simple and functional, a high-stakes challenge for all of them but in particular for the search team, because they're tinkering with the company's main revenue source.

Google has held a dominant position in search usage since the mid-2000s and credits its success to constant improvements to its back-end algorithms.

While it's clear Google must constantly sharpen back-end algorithmic search functions, some might wonder why Google would mess with the user interface (UI) and possibly risk breaking something that may not need fixing.

After all, for its first seven years, Google was the poster child for UI minimalism among Internet companies, adhering to a very conservative design approach and making few visual changes to its search engine.

However, that began to change about four years ago when the company launched its universal search initiative to mesh into its Web search results elements from its vertical engines, like links to photos, videos, books, news and maps.

Google also got bolder in its testing and introduction of new search controls for filtering results, refining queries and amplifying result information.

Now, since co-founder Larry Page took over in April as CEO, he has intensified the call for visual design improvements in the interfaces of Google products, including search.

Unsurprisingly, the search-engine design team conducts extensive research and testing into potential user interface modifications to determine which of these changes merits a wide rollout, two of the team's leaders told IDG News Service in interviews.

"I study how people search in multiple ways to understand how and why they search, what they do and don't understand," said Dan Russell, lead researcher for the User Experience team for Google Search. "I get into the cognition and mental models of what people are doing in search and why."

To accomplish this, Google brings people into its testing facility and conducts extremely detailed and precise research into their actions, including their eye movements. "We study their behavior millisecond by millisecond," Russell said.

These tests are complemented by the more conventional, broader trials, where a new design feature will be rolled out to a small fraction of all Google search users -- say, to 5 percent -- with analysis on the effects it has on that group over days or weeks.

With Google generating most of its revenue from search, Russell and the others who work in search design know that a misguided interface change that harms usage must be avoided at all costs.

"We're very aware that the search engine is Google's crown jewel. It's the heart of the company in many ways," he said.

However, Russell, who has been with Google for about six years, welcomes the company's shift to be bolder with its design. "Especially in the past two years, Google has shifted to be much more experimental with its UI," he said.

For example, in May of last year, Google gave its search results page a major overhaul, adding query refinement and navigation controls in a new, permanent left-hand column that previously people had to click on a link to open, and jazzing up its colors and typefaces.

Google also has added a feature that lets people display a snapshot of a Web results page along the right-hand column of the results page. This feature is represented by a binocular icon placed next to each result.

Most recently, Google increased the prominence and quantity of what it calls sitelinks -- links to specific sections of a website that it shows as subsections for broad query results that aren't specific enough for the search engine to determine where on a site the user should go. This change included increasing the font size of sitelinks and the addition of a one-line snippet description for each one.

Now, Page has intensified the call for UI improvements not only in Google's search engine but across all of its Web applications, like Gmail.

Shortly after becoming CEO, Page assembled all the design chiefs of the different Google services and products and told them he wanted a better yet uniform look for Google interfaces, said Jon Wiley, lead designer on the User Experience team for Google Search.

"Larry is leading on this, so that Google has a coherent design look across all products that's beautiful, simple and effective," Wiley said.

For search, the guiding principle for any UI change is to make it simpler and faster for people to find the information they're looking for. That presents a unique design challenge for people like Wiley, especially with rising user expectations and evolving search scenarios.

"The search engine is this really powerful and complex system that must understand the entire open Web, and we must take all that power and complexity and put a layer on it that makes it really simple for people to use," he said.